ALMA (Atacama Large Millimeter/submillimeter Array)
ALMA (Atacama Large Millimeter/submillimeter Array)
The ALMA Observatory is an international astronomy facility, a partnership of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and NINS (National Institutes of Natural Sciences) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the NRC (National Research Council) of Canada and the NSC (National Science Council) of Taiwan and by NINS of Japan in cooperation with the Academia Sinica (AS) in Taiwan, and KASI (Korea Astronomy and Space Science Institute) Korea. 1) 2)
ALMA construction and operations are led on behalf of Europe by ESO on behalf of its Member States; by NRAO (National Radio Astronomy Observatory), managed by AUI (Associated Universities, Inc.), on behalf of North America; and by NAOJ (National Astronomical Observatory of Japan) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Figure 1: Global partnerships of the ALMA Program (image credit: ALMA partnership) 3)
ALMA isthe largest astronomical project in existence, it is a single telescope of revolutionary design, composed of 66 high precision antennas (forming a sparse array of antennas) of 12 m and 7 m in diameter. ALMA is located at a truly unique and unusual place: the Chilean Atacama desert. While the astronomers will operate the telescope from the OSF (Operations Support Facility) Technical Building, at 2,900 m above sea level, the array of antennas will be located at the Altiplano de Chajnantor, a plateau at an altitude of 5,000 m altitude. This location was selected because of many well justified scientific reasons, particularly dryness and altitude. The ALMA site with the average annual rainfall below 100 mm is the perfect place for a new telescope capable of detecting radio waves just millimeters in wavelength. Indeed, radio waves penetrate a lot of the gas and dust in space, and can pass through the Earth’s atmosphere with little distortion. However, if the atmosphere above ALMA contained water, the radio signals would be heavily absorbed – the tiny droplets of water scatter the radio waves in all directions before they reach the telescope, and would degrade the quality of the observations.
Furthermore, the flat and wide land at the ALMA site is suitable for the construction of a large-scale array. Considering these aspects, the ALMA Observatory will not only be unique because of its ambitious scientific goals, and the unprecedented technical requirements, it will also be unique because of the very specific, harsh environment and living conditions in which the most challenging radio telescope array will operate with high efficiency and accuracy.
ALMA is an international astronomy facility, a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led on behalf of Europe (ESO), North America (NRAO/AUI), and East Asia (NAOJ). The JAO (Joint ALMA Observatory) provides the unified leadership and management of the construction, commissioning and operation of ALMA. The JAO coordinates the ALMA Development Program in order to effectively manage the technological evolution of the ALMA facility. Periodically, solicitations (“calls”) are issued by each of the international partners to identify and fund development initiatives (“upgrades”) which will enhance the performance of the ALMA facility. The implementation of ALMA upgrades are assigned on a competitive basis.
Figure 2: A state-of-the-art telescope to study light with wavelengths of about one millimeter, shining from some of the coldest objects in the Universe, ALMA is a cooperation of the European Southern Observatory (ESO), together with its international partners. The site of ALMA is the 5000-m altitude Chajnantor plateau in northern Chile, one of the driest places on Earth (video credit: ESO, ALMA (ESO/NAOJ/NRAO), C. Malin , P. Horálek, Liam Young, B. Tafreshi, J. J. Tobin (University of Oklahoma/Leiden University), M. Kaufman, Theofanis N. Matsopoulos, H. H. Heyer, S. Argandoña and H. Zodet. Music by Movetwo, Published on Dec 7, 2016)
Figure 3: The Atacama Large Millimeter/submillimeter Array is an astronomical interferometer of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter and submillimeter wavelength operations, the array has been constructed on the Chajnantor plateau at 5,000 metres altitude, near Llano de Chajnantor Observatory and Atacama Pathfinder Experiment (video credit: ESO, Published on Oct 7, 2017)
Major ALMA Facilities
ALMA will be the world’s most powerful telescope for studying the Universe at submillimeter and millimeter wavelengths, on the boundary between infrared light and the longer radio waves. However, ALMA does not resemble many people’s image of a giant telescope. It does not use the shiny, reflective mirrors of visible- and infrared-light telescopes; it is instead comprised of many “antennas” that look like large metallic satellite dishes. 15)
Several antennas have already been installed in the harsh conditions of the 5000 m altitude Chajnantor plateau, and more are under construction at the 2900 m altitude OSF (Operations Support Facility). When ALMA is fully operational, visitors to Chajnantor will encounter 66 antennas, 54 of them with 12 m diameter dishes, and 12 smaller ones, with a diameter of 7 m each.
Figure 4: Photo of the first ALMA 12 m antenna, manufactured by Mitsubishi Electric Corporation (image credit: ALMA ,ESO/NAOJ/NRAO)
The most visible part of each antenna is the dish, a large reflecting surface. Most of ALMA’s dishes have a diameter of 12 m. Each dish plays the same role as the mirror of an optical telescope: it collects radiation coming from distant astronomical objects, and focuses it into a detector that measures the radiation. The difference between the two types of telescopes is the wavelength of the radiation detected. Visible light, captured by optical telescopes, is just a small part of the spectrum of electromagnetic radiation, with wavelengths between roughly 380 and 750 nm. ALMA, in contrast, will probe the sky for radiation at longer wavelengths from a few hundred µm to about 1 mm (about one thousand times longer than visible light). This is known, perhaps unsurprisingly, as mm and sub-mm radiation, and lies at the very short-wavelength end of radio waves.
This longer wavelength range is the reason, why ALMA’s dishes are not mirrors, but have a surface of metallic panels. The reflecting surfaces of any telescope must be virtually perfect: if they have any defects that are larger than a few percent of the wavelength to be detected, the telescope won’t produce accurate measurements. The longer wavelengths that ALMA’s antennas detect mean that although the surfaces are accurate to within 25 µm — much less than the thickness of a single sheet of paper, the dishes do not need the mirror finish used for visible-light telescopes. So although ALMA’s dishes look like giant metallic satellite dishes, to a submillimeter-wavelength photon (light-particle), they are almost perfectly smooth reflecting surfaces, focusing the photons with great precision.
Not only are the dish surfaces carefully controlled, but the antennas can be steered very precisely and pointed to an angular accuracy of 0.6 arcseconds (one arcsecond is 1/3600 of a degree). This is accurate enough to pick out a golf ball at a distance of 15 km.
ALMA will combine the signals from its array of antennas as an interferometer — acting like a single giant telescope as large as the whole array. Thanks to the two antenna transporter vehicles, astronomers will be able to reposition the antennas according to the kind of observations needed. So, unlike a telescope that is constructed and remains in one place, the antennas are robust enough to be picked up and moved between concrete foundation pads without this affecting their precision engineering.
In addition, the antennas achieve all this without the protection of a telescope dome or enclosure. The dishes are exposed to the harsh environmental conditions of the high altitude Chajnantor plateau, with strong winds, intense sunlight, and temperatures between ±20 ºC. Despite Chajnantor being in one of the driest regions on the planet, there is even sometimes snow here, but ALMA’s antennas are designed to survive all these hardships.
The production of the antennas is being shared between the ALMA partners. ESO has ordered twentyfive 12 m antennas, with an option for an additional seven, from the AEM Consortium (Alcatel Alenia Space France, Alcatel Alenia Space Italy, European Industrial Engineering S.r.L., MT Aerospace). The North American partners have placed an order of the same size with Vertex RSI, while the four 12 m and twelve 7 m antennas comprising ALMA’s ACA (Atacama Compact Array) have been ordered by NAOJ from MELCO (Mitsubishi Electric Corporation).
Apart from the obvious difference in size between the 12-meter and 7-meter antennas, careful observers will spot subtle differences in the antenna design from each partner. However, all the antennas are designed to meet the stringent technical specifications, and work together smoothly as parts of the whole. These state-of-the-art dishes, combined in a single revolutionary telescope, reflect the cooperative nature of the global ALMA project.
Figure 5: Photo of the ALMA antenna array (image credit: ALMA partnership, Ref. 3)
Figure 6: The 12th 7 m antenna developed by Japan was delivered to the high site in Chajnantor on April 29, 2013. Now all the 16 antennas of the ACA (Atacama Compact Array) are installed at the Array Operations Site at an altitude of 5,000 m, waiting to unveil secrets of the universe (image credit: ALMA partnership) 16)
Figure 7: The final antenna of the ALMA project is here seen arriving to the high site at the ALMA Observatory, 5000 m above sea level. Its arrival completes the complement of 66 ALMA antennas on the Chajnantor Plateau in the Atacama Desert of northern Chile (image credit: ALMA, ESO/NAOJ/NRAO, A. Marinkovic) 17)
ALMA Front End Integration Centers: A construction project like ALMA, involving several partners in four different continents, requires consensus on several organizational and managerial decisions concerning the actual execution of certain construction activities. Several different scenarios for assembling and integrating the Front End components were extensively studied. This study revealed that the best solution was a “parallel approach”, installing half of the Front End in Europe and the other half in North America with identical and parallel procedures. This scenario was preferred in view of logistics, organization and program risks. Mainly based on considerations of risk mitigation, the parallel FEIC (Front End Integration Centers) was selected. The European FEIC is located at Rutherford Appleton Laboratory (UK) and the North American FEIC at NRAO. A third FEIC is installed in Taiwan to carry out the integration of Front End assemblies required for the antennas supplied by NAOJ.
Figure 8: Aerial view of the ALMA OSF (Operation Support Facility) at 2,900 m altitude (image credit: ALMA partnership)
A world-class observatory site in the desert: 18)
The ALMA Observatory is operated at two distinct sites, far away from comfortable living conditions of modern civilization. The ALMA OSF is the base camp for the every-day, routine operation of the observatory. It is located at an altitude of about 2900 m, quite high compared to standard living conditions, but still quite acceptable for scientific projects in astronomy of similar scope. However, the OSF will not only serve as the location for operating the Joint ALMA Observatory, it is also the AIV (Assembly, Integration and Verification) station for all the high technology equipment before being moved to the AOS (Array Operations Site), located at 5000 m altitude. Antenna assembly is done at the OSF site at three separate areas, one each for the antennas provided by North America (VERTEX), Japan (MELCO), and Europe (AEM Consortium).
The OSF is also the center for activities associated with commissioning and science verification as well as Early Science operation. During the operations phase of the observatory it is the workplace of the astronomers and of the teams responsible for maintaining proper functioning of all the telescopes.
The construction of the OSF and AOS sites and their access required substantial efforts of the ALMA project. Obviously, there was no access to these two remote locations (Figure 9). The OSF site, located at 2900 m altitude, is about 15 km away from the closest public road, the Chilean highway No. 23. The AOS is another 28 km away from the OSF site. Thus, one of the first projects to be accomplished by ALMA was to construct an access road not only to the OSF but also to the AOS road, 43 km in length, not only at high altitudes, but also with sufficient width to regularly transport a large number of large radio telescopes with a diameter of 12 m.
The geographical location of ALMA (at Altiplano de Chajnantor) is latitude: -23.029° ; longitude: -67.755°
ALMA Front End System
The ALMA Front End system is the first element in a complex chain of signal receiving, conversion, processing and recording. The Front End is designed to receive signals of ten different frequency bands. 19)
The ALMA Front End is far superior to any existing systems. Indeed, spin offs of the ALMA prototypes are leading to improved sensitivities in existing millimeter and submillimeter observatories around the world. The Front End units are comprised of numerous elements, produced at different locations in Europe, North America, East Asia and Chile.
ALMA Cryostats: The largest single element of the Front End system is the cryostat (vacuum vessel) with the cryo-cooler attached. The cryostats will house the receivers, which are assembled in cartridges and can relatively easily be installed or replaced. The corresponding warm optics, windows and infrared filters were delivered by the IRAM (Institut de Radio Astronomie Millimétrique) of France. The operating temperature of the cryostats will be as low as 4 K (equivalent to -269ºC).
ALMA Receiver Bands: In the initial phase of operations, the antennas will be equipped with at least four receiver bands: Band 3 (3 mm), Band 6 (1 mm), Band 7 (0.85 mm), Band 9 (0.45 mm). It is planned to equip the antennas with the missing bands at a later stage of ALMA operations. The development programs were successful, as the requirements could be met – and sometimes the performance is even better than defined in the specifications.
Table 2: The 10 frequency bands of the ALMA antennas
Modular Cryogenic Receiver Concept. The complete front end unit will have a diameter of 1 m, be about 1m high and have a mass of about 750 kg. The cryostat will be cooled down to ~4 K by a 3-stage commercial closed-cycle cryocooler based on the Gifford – McMahon cooling cycle. The individual frequency bands are implemented in the form of modular cartridges that will be inserted in a large common cryostat. This cartridge concept allows for a great flexibility in construction and operation of the array. Figure 10 shows an example of such a receiver cartridge. Another advantage of the cartridge layout with well-defined interfaces is the fact that different cartridges can be developed and built by different groups within the ALMA Project with a large degree of independence but without the risk of incompatibility between them. 20)
Figure 10: Example of a, Band 6, receiver cartridge. The larger diameter metal plate in the middle is the boundary between cooled receiver electronics inside the cryostat (right hand side) and the room temperature electronics (left hand side), image credit: ALMA partnership)
Figure 11: Photo of one typical receiver cartridge built for ALMA ((image credit: ALMA partnership)
Band 5 — July 17, 2015: After more than five years of development and construction, ALMA successfully opened its eyes on another frequency range after obtaining the first fringes with a Band 5 receiver, specifically designed to detect water in the local Universe. Band 5 will also open up the possibility of studying complex molecules in star-forming regions and protoplanetary discs, and detecting molecules and atoms in galaxies in the early Universe, looking back about 13 billion years (Ref. 11).
“Band 5 will open up new possibilities to explore the Universe and bring new discoveries,” explains ESO’s Gianni Marconi, who is responsible for the integration of Band 5. “The frequency range of this receiver includes an emission line of water that ALMA will be able to study in nearby regions of star formation. The study of water is, of course, of intense interest because of its role in the origin of life.” With Band 5, ALMA will also be able to probe the emission from ionized carbon from objects seen soon after the Big Bang, opening up the possibility of probing the earliest epoch of galaxy formation. “This band will also enable astronomers to study young galaxies in the early Universe about 500 million years after the Big Bang,” added Gianni Marconi.
The Band 5 receivers were originally designed and prototyped by Onsala Space Observatory's Group for Advanced Receiver Development (GARD) at Chalmers University of Technology in Sweden, in collaboration with the Rutherford Appleton Laboratory, UK, and ESO, under the European Commission supported Framework Program FP6 (ALMA Enhancement). After having successfully tested the prototypes, the first production-type receivers were built and delivered to ALMA by a consortium of NOVA and GARD in the first half of 2015. Two receivers were used for the first light. The remainder of the 73 receivers ordered, including spares, will be delivered between now and 2017.
Figure 12: Photo of one of the Band 5 receiver cartridges built for ALMA. Extremely weak signals from space are collected by the ALMA antennas and focussed onto the receivers, which transform the faint radiation into an electrical signal (image credit: ALMA partnership)
ALMA Back End and Correlator
The ALMA Back End systems deliver signals generated by Front End units installed in each antenna to the Correlator installed in the AOS (Array Operations Site) Technical Building, located at an altitude of 5,000 m. Signal processing and data transfer is schematically shown in Figure 13. Analog data, produced by the Front End electronics, is processed and digitized before entering into the data encoder, followed by the optical transmitter units and multiplexers. All these elements are installed in the receiver cabins of each antenna. Optical signals are then transmitted by fibers to the AOS Technical Building. The total distance is, in one antenna configuration, about 15 km. At the Technical Building the incoming optical signals are de-multiplexed and de-formatted before entering the Correlator. 21) 22) 23)
ALMA main array Correlator: The ALMA main array Correlator, to be installed in the AOS Technical Building, is the last component in the receiving end of the data transmission. It is a very large data processing system, composed of four quadrants, each of which can process data coming from up to 504 pairs of antennas. The complete correlator will have 2912 printed circuit boards, 5200 interface cables, and more than 20 million solder points. Integral parts of the Correlator are TFB (Tunable Filter Bank) cards. The layout is such that four TFB cards are needed for the data coming from a single antenna. The TFB cards have been developed and optimized by the University of Bordeaux over the last few years.
ACA (Atacama Compact Array) Correlator: The ACA Correlator is designed to process the signals detected by the Atacama Compact Array (ACA). This correlator consists of 52 modules connected with each other through optical-fiber cables. All the modules are installed in 8 racks in the AOS Technical Building. The power spectra issued from the correlation are transferred to the ACA data processing computers.
• May 15, 2020: The contract has been signed for the production of the final set of receivers to be installed on the Atacama Large Millimeter/submillimeter Array (ALMA). Of the originally foreseen ten receiver bands, eight have already been installed, and the ninth, Band 1, is currently in production in East-Asia. Now, contracts have been signed to start the production of the final band in the original ALMA definition — Band 2, led by ESO. Exceeding the originally defined frequency range for this Band (69-90 GHz), the proposed receiver will operate at the full 67-116 GHz frequency window. The hugely successful Band 3 receiver has already opened up the 84-116 GHz frequency range years ago, but the new Band 2 will allow for observations across the entire 67-116 GHz atmospheric window using a single receiver. The project will involve multiple international partners as detailed below. 24)
Figure 14: The figure shows the typical contributions of continuum emission sources with respect to the ALMA Band 2 frequency coverage (purple shaded region), and the Band 1 frequency coverage (pink shaded region). ALMA Band 2 will on average span one of the cleanest mm or submm-wave windows available. The grey bands depict the frequency bands of the Planck satellite, which covered similar frequencies as ALMA. Figure adapted from Planck Collaboration et al 2016 (A&A 594, A10 (2016)), image credit: ESO
Following successful tests of a prototype Band 2 receiver (Yagoubov et al. 2020, A&A 634, A46), the ALMA board has approved the pre-production of a series of six cartridges, with the goal of eventually moving into the production of the full set, one for each of the ALMA antennas. This will depend on the verification of the performance and series production readiness based on the pre-production receiver cartridges.
The 67-116 GHz atmospheric window is rich in strong molecular lines with less crowding than other atmospheric windows. Due to the relatively low excitation energies, these lines are exceptionally suited for studying the dense molecular gas and early phases of star formation. Furthermore, the window is rich in complex organic molecules (COMs), tying in directly with the new fundamental science drivers defined in the ALMA 2030 Development Roadmap. Band 2 will also fill a gap in ALMA's ability to observe the molecular reservoir in redshifted galaxies. Finally, Band 2 continuum measurements have the lowest intrinsic background, as thermal dust emission, CMB emission, free-free emission and synchrotron emission conspire to form a local emission minimum in frequency space.
The production of the Band 2 receiver cartridges will be undertaken by a consortium comprising the Netherlands Research School for Astronomy (NOVA), Chalmers University, Gothenburg, Sweden, and the Italian National Institute for Astrophysics (INAF). The National Astronomical Observatory of Japan (NAOJ) will contribute to the production and testing of receiver optics as an East Asia contribution to the ALMA Development Program. The National Radio Astronomy Observatory (NRAO) and the University of Chile have been involved in the development and production of some components of the receivers, which will be sent to ESO for testing and integration.
ALMA links with other observatories to create an Earth-size telescope
November 2015: ALMA continues to expand its power and capabilities by linking with other millimeter-wavelength telescopes in Europe and North American in a series of VLBI (Very Long Baseline Interferometry) observations. In VLBI, data from two or more telescopes are combined to form a single virtual telescope that spans the geographic distance between them. The most recent of these experiments with ALMA formed an Earth-size telescope with extraordinarily fine resolution. 25)
Figure 15: ALMA combined its power with IRAM and VLBA in VLBI separated observations (image credit: A. Angelich, NRAO/AUI/NSF)
These experiments are an essential step in including ALMA in the EHT (Event Horizon Telescope), a global network of millimeter-wavelength telescopes that will have the power to study the supermassive black hole at the center of the Milky Way in unprecedented detail.
Before ALMA could participate in VLBI observations, it first had to be upgraded adding a new capability known as a phased array. This new version of ALMA allows its 66 antennas to function as a single radio dish 85 m in diameter, which then becomes one element in a much larger VLBI telescope.
• The first test of ALMA’s VLBI capabilities occurred on 13 January 2015, when ALMA successfully linked with the APEX (Atacama Pathfinder Experiment Telescope), which is about two kilometers from the center of the ALMA array.
• On 30 March 2015, ALMA reached out much further by linking with IRAM (Institut de Radioastronomie Millimetrique), the 30 m radio telescope in the Sierra Nevada of southern Spain. Together they simultaneously observed the bright quasar 3C 273. Data from this observation were combined into a single observation with a resolution of 34 µarcsec (1 microarcsecond = 2.8º x 10-10). This is equivalent to distinguish an object of less than 10 cm on the Moon, seen from Earth. - The March observations were made during an observing campaign of the EHT at a wavelength of 1.3 mm.
• The most recent VLBI observing run was performed on 1–3 August 2015 with six of the VLBA (Very Long Baseline Array) antennas of NRAO (National Radio Astronomy Observatory). This combined instrument formed a virtual Earth-size telescope and observed the quasar 3C 454.3, which is one of the brightest radio beacons on the sky, despite lying at a distance of 7.8 billion light-years. These data were first processed at NRAO and MIT-Haystack in the United States and further post-processing analysis is being performed at the MPIfR (Max Planck Institute for Radio Astronomy) in Bonn, Germany.
- The VLBA is an array of 10 antennas spread across the United States from Hawaii to St. Croix. For this observation, six antennas were used: North Liberty, IA; Fort Davis, TX; Los Alamos, NM; Owens Valley, CA; Brewster, WA; and Mauna Kea, HI. The observing wavelength was 3 mm.
• The new observations are a further step towards global interferometric observations with ALMA in the framework of the Global mm-VLBI Array and the EHT (Event Horizon Telescope), with ALMA as the largest and the most sensitive element. The addition of ALMA to millimeter VLBI will boost the imaging sensitivity and capabilities of the existing VLBI arrays by an order of magnitude.
Note: As of 19 March 2020, the previously single large ALMA file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the ALMA project mission and its imagery in the period 2020 and 2019, in addition to some of the mission milestones.
Some status and selected observation imagery provided by ALMA in 2020-2019
• September 18, 2020: Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a set of stellar winds around aging stars and present an explanation for the mesmerizing shapes of planetary nebulae. Contrary to common consensus, the team found that stellar winds are not spherical but have a form similar to that of planetary nebulae. The team concludes that interaction with an accompanying star or exoplanet shapes both the stellar winds and planetary nebulae. The findings were published in Science. 28) 29) 30)
- Dying stars swell and cool to eventually become red giants. They produce stellar winds, flows of particles that the star expels, which causes them to lose mass. Because detailed observations were lacking, astronomers have always assumed that these winds were spherical, like the stars they surround. As the star evolves further, it heats up again, and the stellar radiation causes the expanding ejected layers of stellar material to glow, forming a planetary nebula.
- For centuries, astronomers were in the dark about the extraordinary variety of colorful shapes observed in planetary nebulas. The nebulae all seem to have a certain symmetry but are rarely round. “The Sun – which will ultimately become a red giant – is as round as a billiard ball, so we wondered: how can such a star produce all these different shapes?” says corresponding author Leen Decin (KU Leuven).
- Her team observed stellar winds around cool red giant stars with the ALMA observatory in Chile, the world’s largest radio telescope. For the first time, they gathered an extensive, detailed collection of observations. Each of them made using the same method, crucial to compare the data, and exclude biases directly.
- What the astronomers saw surprised them. “We noticed these winds are anything but symmetrical or round,” Professor Decin says. “Some of them are quite similar in shape to planetary nebulae.”
Figure 16: This image gallery of stellar winds around cool ageing stars shows a variety of morphologies, including disks, cones, and spirals. The blue color represents material that is coming towards you; red is material that is moving away from you (image credit: L. Decin, ESO/ALMA)
- The researchers could even identify different categories of shapes. “Some stellar winds were disk-shaped, others contained spirals, and we identified cones in a third group.” This is a clear indication that the shapes weren’t created randomly. The team realized that other low-mass stars or even heavy planets in the dying star’s vicinity were causing the different patterns. These companions are too small and dim to detect directly. “Just like how a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind,” Decin explains.
- The team put this theory into models, and indeed: the shape of the stellar winds can be explained by the companions surrounding them. The rate at which the cool evolved star is losing its mass due to the stellar wind is an important parameter.
- Up until now, calculations about the evolution of stars were based on the assumption that aging Sun-like stars have spherical stellar winds. “Our findings change a lot. Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimate of old stars could be wrong by up to a factor of 10.” The team is now doing further research to see how this might impact calculations of other crucial characteristics of stellar and galactic evolution.
- The study also helps envision what the Sun might look like when it dies in 7000 million years. “Jupiter or even Saturn – because they have such a big mass – are going to influence whether the Sun spends its last millennia at the heart of a spiral, a butterfly, or any of the other entrancing shapes we see in planetary nebulae today,” Decin notes. “Our calculations now indicate that a weak spiral will form in the stellar wind of the old dying Sun.”
- “We were very excited when we explored the first images,” says co-author Miguel Montargès (KU Leuven). “Each star, which was only a number before, became an individual by itself. Now, to us, they have their own identity. This is the magic of having high-precision observations: stars are no longer just points anymore.”
- The study is part of the ATOMIUM project, which aims to learn more about the physics and chemistry of old stars. “Cool aging stars are considered boring, old and simple, but we now prove that they are not: they tell the story of what comes after. It took us some time to realize that stellar winds can have the shape of rose petals (see, for example, the stellar wind of R Aquilae). But, as Antoine de Saint-Exupéry said in his book Le Petit Prince: ‘C’est le temps que tu as perdu pour ta rose, qui fait ta rose si importante’ – ‘It’s the time you spent on your rose that makes your rose so important,'” Decin concludes.
• August 12, 2020: Astronomers using the ALMA (Atacama Large Millimeter/submillimeter Array), in which the European Southern Observatory (ESO) is a partner, have revealed an extremely distant and therefore very young galaxy that looks surprisingly like our Milky Way. The galaxy is so far away its light has taken more than 12 billion years to reach us: we see it as it was when the Universe was just 1.4 billion years old. It is also surprisingly unchaotic, contradicting theories that all galaxies in the early Universe were turbulent and unstable. This unexpected discovery challenges our understanding of how galaxies form, giving new insights into the past of our Universe. 31)
- “This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” says Francesca Rizzo, PhD student from the Max Planck Institute for Astrophysics in Germany, who led the research published today in Nature. While the galaxy the astronomers studied, called SPT0418-47, doesn’t appear to have spiral arms, it has at least two features typical of our Milky Way: a rotating disc and a bulge, the large group of stars packed tightly around the galactic center. This is the first time a bulge has been seen this early in the history of the Universe, making SPT0418-47 the most distant Milky Way look-alike.
- “The big surprise was to find that this galaxy is actually quite similar to nearby galaxies, contrary to all expectations from the models and previous, less detailed, observations,” says co-author Filippo Fraternali, from the Kapteyn Astronomical Institute, University of Groningen in the Netherlands. In the early Universe, young galaxies were still in the process of forming, so researchers expected them to be chaotic and lacking the distinct structures typical of more mature galaxies like the Milky Way.
- Studying distant galaxies like SPT0418-47 is fundamental to our understanding of how galaxies formed and evolved. This galaxy is so far away we see it when the Universe was just 10% of its current age because its light took 12 billion years to reach Earth. By studying it, we are going back to a time when these baby galaxies were just beginning to develop.
Figure 17: Astronomers using ALMA, in which the ESO is a partner, have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light (image credit: ALMA (ESO/NAOJ/NRAO), Rizzo et al.)
- Because these galaxies are so far away, detailed observations with even the most powerful telescopes are almost impossible as the galaxies appear small and faint. The team overcame this obstacle by using a nearby galaxy as a powerful magnifying glass — an effect known as gravitational lensing — allowing ALMA to see into the distant past in unprecedented detail. In this effect, the gravitational pull from the nearby galaxy distorts and bends the light from the distant galaxy, causing it to appear misshapen and magnified.
- The gravitationally lensed, distant galaxy appears as a near-perfect ring of light around the nearby galaxy, thanks to their almost exact alignment. The research team reconstructed the distant galaxy’s true shape and the motion of its gas from the ALMA data using a new computer modelling technique. “When I first saw the reconstructed image of SPT0418-47 I could not believe it: a treasure chest was opening,” says Rizzo.
- “What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe,” stated co-author Simona Vegetti, also from the Max Planck Institute for Astrophysics. “This result is quite unexpected and has important implications for how we think galaxies evolve." The astronomers note, however, that even though SPT0418-47 has a disc and other features similar to those of spiral galaxies we see today, they expect it to evolve into a galaxy very different from the Milky Way, and join the class of elliptical galaxies, another type of galaxies that, alongside the spirals, inhabit the Universe today.
- This unexpected discovery suggests the early Universe may not be as chaotic as once believed and raises many questions on how a well-ordered galaxy could have formed so soon after the Big Bang. This ALMA finding follows the earlier discovery announced in May of a massive rotating disc seen at a similar distance. SPT0418-47 is seen in finer detail, thanks to the lensing effect, and has a bulge in addition to a disc, making it even more similar to our present-day Milky Way than the one studied previously.
- Future studies, including with ESO’s Extremely Large Telescope, will seek to uncover how typical these ‘baby’ disc galaxies really are and whether they are commonly less chaotic than predicted, opening up new avenues for astronomers to discover how galaxies evolved. 32)
• July 9, 2020: At this time, the COVID-19 pandemic continues to affect the lives of ALMA staff and users around the world. Although in some of the ALMA regions the situation is slowly improving, in other regions, including Chile, the evolution of the outbreak remains highly uncertain. 33)
- Because of the on-going situation in Chile, ALMA operations unfortunately remain suspended. ALMA staff continue to monitor the situation very carefully and work on the development of detailed plans for the return to operations, which will be initiated when the situation allows. We will keep updating the user community on the developments.
- Northern Chile was recently hit by a magnitude 6.8 earthquake. Fortunately this caused no injuries to ALMA staff and no serious damage at the ALMA site. This was followed by extremely high winds, that led to some minor damage at the ALMA OSF (Operations Support Facility).
- As always, the ALMA Regional Centers provide support to their respective communities, and can assist in the analysis of your data and help with archive research projects. If you have any questions on this, or comments or concerns related to the situation at ALMA, please contact the ALMA helpdesk.
• July 2, 2020: Astronomers created a stunning new image showing celestial fireworks in star cluster G286.21+0.17. 34)
- Most stars in the universe, including our Sun, were born in massive star clusters. These clusters are the building blocks of galaxies, but their formation from dense molecular clouds is still largely a mystery.
- The image of cluster G286.21+0.17 (Figure 18) is a multiwavelength mosaic. The cluster is located in the Carina region of our galaxy, about 8000 light-years away.
Figure 18: Star cluster G286.21+0.17, caught in the act of formation. This is a multiwavelength mosaic of more than 750 ALMA radio images, and 9 Hubble infrared images. ALMA shows molecular clouds (purple) and Hubble shows stars and glowing dust (yellow and red), image credit: ALMA (ESO/NAOJ/NRAO), Y. Cheng et al.; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble)
- Dense clouds made of molecular gas (purple ‘fireworks streamers’) are revealed by ALMA. The telescope observed the motions of turbulent gas falling into the cluster, forming dense cores that ultimately create individual stars.
- The stars in the image are revealed by their infrared light, as seen by Hubble, including a large group of stars bursting out from one side of the cloud. The powerful winds and radiation from the most massive of these stars are blasting away the molecular clouds, leaving faint wisps of glowing, hot dust (shown in yellow and red).
- “This image shows stars in various stages of formation within this single cluster,” said Yu Cheng of the University of Virginia in Charlottesville, Virginia, and lead author of two papers published in The Astrophysical Journal. 35) 36)
- Hubble revealed about a thousand newly-formed stars with a wide range of masses. Additionally, ALMA showed that there is a lot more mass present in dense gas that still has to undergo collapse. “Overall the process may take at least a million years to complete,” Cheng added.
- “This illustrates how dynamic and chaotic the process of star birth is,” said co-author Jonathan Tan of Chalmers University in Sweden and the University of Virginia and principal investigator of the project. “We see competing forces in action: gravity and turbulence from the cloud on one side, and stellar winds and radiation pressure from the young stars on the other. This process sculpts the region. It is amazing to think that our own Sun and planets were once part of such a cosmic dance.”
- “The phenomenal resolution and sensitivity of ALMA are evident in this stunning image of star formation,” said Joe Pesce, NSF Program Officer for NRAO/ALMA. “Combined with the Hubble Space Telescope data we can clearly see the power of multiwavelength observations to help us understand these fundamental universal processes.”
• July 6, 2020: The molecular gas in galaxies is organized into a hierarchy of structures. The molecular material in giant molecular gas clouds travels along intricate networks of filamentary gas lanes towards the congested centers of gas and dust where it is compressed into stars and planets, much like the millions of people commuting to cities for work around the world. To better understand this process, a team of astronomers led by Jonathan Henshaw at Max Planck Institute for Astronomy (MPIA) have measured the motion of gas flowing from galaxy scales down to the scales of the gas clumps within which individual stars form. Their results show that the gas flowing through each scale is dynamically interconnected: while star and planet formation occurs on the smallest scales, this process is controlled by a cascade of matter flows that begin on galactic scales. These results are published today in the scientific journal Nature Astronomy. 37) 38)
- The scientists use data from the following observatories: Atacama Large Millimeter/submillimeter Array (ALMA), Morita Atacama Compact Array, Five College Radio Astronomy Observatory (FCRAO), Institut de Radioastronomie Millimétrique (IRAM) Plateau de Bure Interferometer, Mopra Radio Telescope, and HSO (Herschel Space Observatory).
- The molecular gas in galaxies is set into motion by physical mechanisms such as galactic rotation, supernova explosions, magnetic fields, turbulence, and gravity, shaping the structure of the gas. Understanding how these motions directly impact star and planet formation is difficult, because it requires quantifying gas motion over a huge range in spatial scale, and then linking this motion to the physical structures we observe. Modern astrophysical facilities now routinely map huge areas of the sky, with some maps containing millions of pixels, each with hundreds to thousands of independent velocity measurements. As a result, measuring these motions is both scientifically and technologically challenging.
- In order to address these challenges, an international team of researchers led by Jonathan Henshaw at the MPIA in Heidelberg set out to measure gas motions throughout a variety of different environments using observations of the gas in the Milky Way and a nearby galaxy. They detect these motions by measuring the apparent change in the frequency of light emitted by molecules caused by the relative motion between the source of the light and the observer; a phenomenon known as the Doppler effect. By applying novel software designed by Henshaw and Ph.D. student Manuel Riener (a co-author on the paper; also at MPIA), the team were able to analyze millions of measurements. “This method allowed us to visualize the interstellar medium in a new way,” says Henshaw.
- The researchers found that cold molecular gas motions appear to fluctuate in velocity, reminiscent in appearance of waves on the surface of the ocean. These fluctuations represent gas motion. “The fluctuations themselves weren’t particularly surprising, we know that the gas is moving,” says Henshaw. Steve Longmore, co-author of the paper, based at Liverpool John Moores University, adds, “What surprised us was how similar the velocity structure of these different regions appeared. It didn’t matter if we were looking at an entire galaxy or an individual cloud within our own galaxy, the structure is more or less the same.”
- To better understand the nature of the gas flows, the team selected several regions for close examination, using advanced statistical techniques to look for differences between the fluctuations. By combining a variety of different measurements, the researchers were able to determine how the velocity fluctuations depend on the spatial scale.
Figure 19: Image of the molecular gas (carbon monoxide) distribution in the southern spiral arm of the galaxy NGC 4321 spanning roughly 15,000 light years across. The bright spots indicate giant molecular clouds that are semi-regularly spaced inside the ridge of more dilute gas inside the spiral arm. The cyan circles depict the locations of star forming complexes (image credit: J. Henshaw/MPIA)
- “A neat feature of our analysis techniques is that they are sensitive to periodicity,” explains Henshaw. “If there are repeating patterns in your data, such as equally spaced giant molecular clouds along a spiral arm, we can directly identify the scale on which the pattern repeats.” The team identified three filamentary gas lanes, which, despite tracing vastly different scales, all seemed to show structure that was roughly equidistantly spaced along their crests, like beads on a string, whether it was giant molecular clouds along a spiral arm or tiny “cores” forming stars along a filament.
- The team discovered that the velocity fluctuations associated with equidistantly spaced structure all showed a distinctive pattern. “The fluctuations look like waves oscillating along the crests of the filaments, they have a well-defined amplitude and wavelength,” says Henshaw adding, “The periodic spacing of the giant molecular clouds on large-scales or individual star-forming cores on small-scales is probably the result of their parent filaments becoming gravitationally unstable. We believe that these oscillatory flows are the signature of gas streaming along spiral arms or converging towards the density peaks, supplying new fuel for star formation.”
- In contrast, the team found that the velocity fluctuations measured throughout giant molecular clouds, on scales intermediate between entire clouds and the tiny cores within them, show no obvious characteristic scale. Diederik Kruijssen, co-author of the paper based at Heidelberg University explains: “The density and velocity structures that we see in giant molecular clouds are ‘scale-free’, because the turbulent gas flows generating these structures form a chaotic cascade, revealing ever smaller fluctuations as you zoom in – much like a Romanesco broccoli, or a snowflake. This scale-free behavior takes place between two well-defined extremes: the large scale of the entire cloud, and the small scale of the cores forming individual stars. We now find that these extremes have well-defined characteristic sizes, but in between them chaos rules.”
Figure 20: Visualization of the observed velocity flows in the spiral galaxy NGC 4321, measured using the radio emission of the molecular gas (carbon monoxide): along the vertical axis, this image shows the velocities of the gas, while the horizontal axis represents the spatial extent of the galaxy. The wave-like oscillations in gas velocity are visible throughout the galaxy (image credit: T. Müller/J. Henshaw/MPIA)
• June 16, 2020: An international team of astronomers has created the most detailed map yet of the atmosphere of the red supergiant star Antares. The unprecedented sensitivity and resolution of both the Atacama Large Millimeter/submillimeter Array (ALMA) and the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) revealed the size and temperature of Antares’ atmosphere from just above the star’s surface, throughout its chromosphere, and all the way out to the wind region. 39) 40)
- Red supergiant stars, like Antares and its more well-known cousin Betelgeuse, are huge, relatively cold stars at the end of their lifetime. They are on their way to run out of fuel, collapse, and become supernovae. Through their vast stellar winds, they launch heavy elements into space, thereby playing an important role in providing the essential building blocks for life in the universe. But it is a mystery how these enormous winds are launched. A detailed study of the atmosphere of Antares, the closest supergiant star to Earth, provides a crucial step towards an answer.
- The ALMA and VLA map of Antares is the most detailed radio map yet of any star, other than the Sun. ALMA observed Antares close to its surface (its optical photosphere) in shorter wavelengths, and the longer wavelengths observed by the VLA revealed the star’s atmosphere further out. As seen in visible light, Antares’ diameter is approximately 700 times larger than the Sun. But when ALMA and the VLA revealed its atmosphere in radio light, the supergiant turned out to be even more gigantic.
- “The size of a star can vary dramatically depending on what wavelength of light it is observed with,” explained Eamon O’Gorman of the Dublin Institute for Advanced Studies in Ireland and lead author of the study published in the June 16 edition of the journal Astronomy & Astrophysics. “The longer wavelengths of the VLA revealed the supergiant’s atmosphere out to nearly 12 times the star’s radius.”
Figure 21: Radio images of Antares with ALMA and the VLA. ALMA observed Antares close to its surface in shorter wavelengths, and the longer wavelengths observed by the VLA revealed the star’s atmosphere further out. In the VLA image a huge wind is visible on the right, ejected from Antares and lit up by its smaller but hotter companion star Antares B (image credit: ALMA (ESO/NAOJ/NRAO), E. O’Gorman; NRAO/AUI/NSF, S. Dagnello)
- The radio telescopes measured the temperature of most of the gas and plasma in Antares’ atmosphere. Most noticeable was the temperature in the chromosphere. This is the region above the star’s surface that is heated up by magnetic fields and shock waves created by the vigorous roiling convection at the stellar surface – much like the bubbling motion in a pot of boiling water. Not much is known about chromospheres, and this is the first time that this region has been detected in radio waves.
Figure 22: Artist impression of the atmosphere of Antares. As seen with the naked eye (up until the photosphere), Antares is around 700 times larger than our sun, big enough to fill the solar system beyond the orbit of Mars (Solar System scale shown for comparison). But ALMA and VLA showed that its atmosphere, including the lower and upper chromosphere and wind zones, reaches out 12 times farther than that (image credit: NRAO/AUI/NSF, S. Dagnello)
- Thanks to ALMA and the VLA, the scientists discovered that the star’s chromosphere extends out to 2.5 times the star’s radius (our Sun’s chromosphere is only 1/200th of its radius). They also found that the temperature of the chromosphere is lower than previous optical and ultraviolet observations have suggested. The temperature peaks at 3,500 degrees Celsius (6,400 degrees Fahrenheit), after which it gradually decreases. As a comparison, the Sun’s chromosphere reaches temperatures of almost 20,000 degrees Celsius.
- “We found that the chromosphere is ‘lukewarm’ rather than hot, in stellar temperatures,” said O’Gorman. “The difference can be explained because our radio measurements are a sensitive thermometer for most of the gas and plasma in the star’s atmosphere, whereas past optical and ultraviolet observations were only sensitive to very hot gas and plasma.”
- “We think that red supergiant stars, such as Antares and Betelgeuse, have an inhomogeneous atmosphere,” said co-author Keiichi Ohnaka of the Universidad Católica del Norte in Chile who previously observed Antares’ atmosphere in infrared light. “Imagine that their atmospheres are a painting made out of many dots of different colors, representing different temperatures. Most of the painting contains dots of the lukewarm gas that radio telescopes can see, but there are also cold dots that only infrared telescopes can see, and hot dots that UV telescopes see. At the moment we can’t observe these dots individually, but we want to try that in future studies.”
- In the ALMA and VLA data, astronomers for the first time saw a clear distinction between the chromosphere and the region where winds start to form. In the VLA image, a huge wind is visible, ejected from Antares and lit up by its smaller but hotter companion star Antares B.
- “When I was a student, I dreamt of having data like this,” said co-author Graham Harper of the University of Colorado, Boulder. “Knowing the actual sizes and temperatures of the atmospheric zones gives us a clue of how these huge winds start to form and how much mass is being ejected.”
- “Our innate understanding of the night sky is that stars are just points of light. The fact we can map the atmospheres of these supergiant stars in detail, is a true testament to technological advances in interferometry. These tour de force observations bring the universe close, right into our own backyard,” said Chris Carilli of the National Radio Astronomy Observatory, who was involved in the first observations of Betelgeuse at multiple radio wavelengths with the VLA in 1998.
• June 9, 2020: High-resolution observations of a young star forming system clearly unveil a pair of protostars at their earliest stages of evolution deeply embedded within the source IRAS 16293-2422 in the Ophiuchus molecular cloud. The team led by the MPE (Max Planck Institute for Extraterrestrial Physics) in Garching, Germany, used the ALMA interferometer not only to pin down the source configuration, but also to measure the gas and stellar kinematics, determining the mass of the young binary. The two close protostars are somewhat heavier than previously thought and they revolve around each other once in about 400 years. 41)
- The system called IRAS 16293-2422 is one of the brightest star-forming regions in our neighborhood. It is located in the Ophiuchus molecular cloud at a distance of about 460 light-years and has been widely studied, also because it shows strong emission of numerous complex organic molecules, building blocks of pre-biotic species. However, until now the detailed configuration of the region was unclear, with observations at different wavelengths showing multiple compact sources at slightly different locations. This confusion was due to the large amount of material in front of the nascent protostars, expected at these earliest stages of formation.
- An international team of astronomers led by the Max Planck Institute for Extraterrestrial Physics (MPE) has now obtained high-resolution radio observations with the ALMA interferometer, which clearly reveals two compact sources A1 and A2 in addition to the well-known protostar B (see Figure 23). “Our observations confirm the location of the two close protostars and reveal that each is surrounded by a very small dust disk. Both, in turn, are in turn embedded in a large amount of material showing complex patterns” remarks María José Maureira from MPE, the lead author of the study. 42)
Figure 23: Zoom into the Ophiuchus molecular cloud, highlighting the star forming system IRAS 16293-2422 with the protostar B in the upper right corner and the now clearly identified protostars A1 and A2 on the bottom left. The binary system is shown also in a further zoom-in panel (image credit: MPE; background: ESO/Digitized Sky Survey 2, Davide De Martin)
Figure 24: Detailed view of the binary protostar system with a size comparison to our solar system. The separation between the sources A1 and A2 is roughly the diameter of the Pluto orbit. The size of the disk around A1 (unresolved) is about the diameter of the asteroid belt. The size of the disk around A2 is about the diameter of the Saturn orbit (image credit: MPE)
- The source A1 has a mass of a bit less than 1 solar mass and is embedded in a small dust disk about the size of the asteroid belt; the source A2 has a mass of about 1.4 solar masses and is embedded in a somewhat larger disk (see Figure 24). Interestingly, this disk around A2 also appears at an angle compared to the overall orientation of the larger cloud structure, while the disk around the source B – at a much larger distance – is seen face-on, indicating a rather chaotic formation history.
- In addition to direct imaging of the dust emission, the team also obtained information on the motion of the gas around the stars through observations of spectral lines of organic molecules, which well trace the high-density region surrounding the discovered binary system. This allowed them to get an independent mass measurement and to confirm that A1 and A2 form a bound pair.
- Combining their latest observations with data collected over the past 30 years, the team found that the two stars orbit each other once every 360 years at a distance similar to the extent of Pluto’s orbit, where the orbit is tilted by about 60° (see Figure 25). “This is the first time that we were able to derive the full orbital parameters of a binary system at this early stage of star formation,” points out Jaime Pineda from MPE, who contributed to the modelling.
- “With these results we are finally able to dive into one of the most embedded and youngest proto-stellar systems, unveiling its dynamical structure and complex morphology, where we clearly see filamentary material connecting the circumstellar disks to the surrounding region and likely to the cirbumbinary disk. The small disks are probably still being fed and growing!” emphasizes Paola Caselli, director at MPE and head of the Center for Astrochemical Studies. “This was only possible thanks to the great sensitivity of ALMA and the observations of molecules which uniquely trace these dense regions. Molecules send us signals at very specific frequencies, and, following changes of such frequencies across the region (due to internal motions) one can reconstruct the complex kinematics of the system. This is the power of astrochemistry.”
Figure 25: Relative motion of A1 (blue) with respect to A2 (red) overlaid on the ALMA continuum observation. The visual impression that A1 orbits around A2 is confirmed through a detailed analysis of the motion of the protostars over a 30-year period (image credit: MPE)
• May 22, 2020: Astronomers of NAOJ (National Astronomy Observatory, Japan) and Keio University using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*. The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity. 43)
- “It has been known that Sgr A* sometimes flares up in millimeter wavelength,” tells Yuhei Iwata, the lead author of the paper published in the Astrophysical Journal Letters and a graduate student at Keio University, Japan. “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”
- Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.
- The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.
- The team focused on short timescale variations and found that the variation period of 30 minutes is comparable to the orbital period of the innermost edge of the accretion disk with the radius of 0.2 astronomical units (1 astronomical unit corresponds to the distance between the Earth and the Sun: 150 million kilometers). For comparison, Mercury, the solar system’s innermost planet, circles around the Sun at a distance of 0.4 astronomical units. Considering the colossal mass at the center of the black hole, its gravity effect is also extreme in the accretion disk.
- “This emission could be related with some exotic phenomena occurring at the very vicinity of the supermassive black hole,” says Tomoharu Oka, a professor at Keio University.
Figure 26: Artist’s impression of the gaseous disk around the supermassive black hole. Hot spots circling around the black hole could produce the quasi-periodic millimeter emission detected with ALMA (image credit: Keio University)
- Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.
- The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole. 44)
• May 20, 2020: In our 13.8 billion-year-old universe, most galaxies like our Milky Way form gradually, reaching their large mass relatively late. But a new discovery made with the Atacama Large Millimeter/submillimeter Array (ALMA) of a massive rotating disk galaxy, seen when the universe was only ten percent of its current age, challenges the traditional models of galaxy formation. This research appears on 20 May 2020 in the journal Nature. 45) 46)
- Galaxy DLA0817g, nicknamed the Wolfe Disk after the late astronomer Arthur M. Wolfe, is the most distant rotating disk galaxy ever observed. The unparalleled power of ALMA made it possible to see this galaxy spinning at 170 miles (272 kilometers) per second, similar to our Milky Way.
- “While previous studies hinted at the existence of these early rotating gas-rich disk galaxies, thanks to ALMA we now have unambiguous evidence that they occur as early as 1.5 billion years after the Big Bang,” said lead author Marcel Neeleman of the Max Planck Institute for Astronomy in Heidelberg, Germany.
How did the Wolfe Disk form?
- The discovery of the Wolfe Disk provides a challenge for many galaxy formation simulations, which predict that massive galaxies at this point in the evolution of the cosmos grew through many mergers of smaller galaxies and hot clumps of gas.
- “Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often ‘violent’ merging,” explained Neeleman. “These hot mergers make it difficult to form well-ordered, cold rotating disks like we observe in our present universe.”
- In most galaxy formation scenarios, galaxies only start to show a well-formed disk around 6 billion years after the Big Bang. The fact that the astronomers found such a disk galaxy when the universe was only ten percent of its current age, indicates that other growth processes must have dominated.
- “We think the Wolfe Disk has grown primarily through the steady accretion of cold gas,” said J. Xavier Prochaska, of the University of California, Santa Cruz and coauthor of the paper. “Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk.”
Figure 27: Artist's impression of the Wolfe Disk, a massive rotating disk galaxy in the early, dusty universe. The galaxy was initially discovered when ALMA examined the light from a more distant quasar (top left), image credit: NRAO/AUI/NSF, S. Dagnello
- The team also used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) and the NASA/ESA Hubble Space Telescope to learn more about star formation in the Wolfe Disk. In radio wavelengths, ALMA looked at the galaxy’s movements and mass of atomic gas and dust while the VLA measured the amount of molecular mass – the fuel for star formation. In UV-light, Hubble observed massive stars. “The star formation rate in the Wolfe Disk is at least ten times higher than in our own galaxy,” explained Prochaska. “It must be one of the most productive disk galaxies in the early universe.”
A ‘normal’ galaxy
- The Wolfe Disk was first discovered by ALMA in 2017. Neeleman and his team found the galaxy when they examined the light from a more distant quasar. The light from the quasar was absorbed as it passed through a massive reservoir of hydrogen gas surrounding the galaxy – which is how it revealed itself. Rather than looking for direct light from extremely bright, but more rare galaxies, astronomers used this ‘absorption’ method to find fainter, and more ‘normal’ galaxies in the early universe.
- “The fact that we found the Wolfe Disk using this method, tells us that it belongs to the normal population of galaxies present at early times,” said Neeleman. “When our newest observations with ALMA surprisingly showed that it is rotating, we realized that early rotating disk galaxies are not as rare as we thought and that there should be a lot more of them out there.”
- “This observation epitomizes how our understanding of the universe is enhanced with the advanced sensitivity that ALMA brings to radio astronomy,” said Joe Pesce, astronomy program director at the National Science Foundation, which funds the telescope. “ALMA allows us to make new, unexpected findings with almost every observation.”
- The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Figure 28: ALMA radio image of the Wolfe Disk, seen when the universe was only ten percent of its current age (image credit: ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello)
• March 19, 2020: Astronomers using ALMA have found striking orbital geometries in protoplanetary disks around binary stars. While disks orbiting the most compact binary star systems share very nearly the same plane, disks encircling wide binaries have orbital planes that are severely tilted. These systems can teach us about planet formation in complex environments. 47)
- In the last two decades, thousands of planets have been found orbiting stars other than our Sun. Some of these planets orbit two stars, just like Luke Skywalker’s home Tatooine. Planets are born in protoplanetary disks – we now have wonderful observations of these thanks to ALMA – but most of the disks studied so far orbit single stars. ‘Tatooine’ exoplanets form in disks around binary stars, so-called circumbinary disks.
- Studying the birthplaces of ‘Tatooine’ planets provides a unique opportunity to learn about how planets form in different environments. Astronomers already know that the orbits of binary stars can warp and tilt the disk around them, resulting in a circumbinary disk misaligned relative to the orbital plane of its host stars. For example, in a 2019 study led by Grant Kennedy of the University of Warwick, UK, ALMA found a striking circumbinary disk in a polar configuration.
- “With our study, we wanted to learn more about the typical geometries of circumbinary disks,” said astronomer Ian Czekala of the University of California at Berkeley. Czekala and his team used ALMA data to determine the degree of alignment of nineteen protoplanetary disks around binary stars. “The high resolution ALMA data was critical for studying some of the smallest and faintest circumbinary disks yet,” said Czekala.
- “We see a clear overlap between the small disks, orbiting compact binaries, and the circumbinary planets found with the Kepler mission,” Czekala said. Because the primary Kepler mission lasted 4 years, astronomers were only able to discover planets around binary stars that orbit each other in fewer than 40 days. And all of these planets were aligned with their host star orbits. A lingering mystery was whether there might be many misaligned planets that Kepler would have a hard time finding. “With our study, we now know that there likely isn’t a large population of misaligned planets that Kepler missed, since circumbinary disks around tight binary stars are also typically aligned with their stellar hosts,” added Czekala.
- Still, based on this finding, the astronomers conclude that misaligned planets around wide binary stars should be out there and that it would be an exciting population to search for with other exoplanet-finding methods like direct imaging and microlensing. (NASA’s Kepler mission used the transit method, which is one of the ways to find a planet.)
Figure 29: The astronomers compared the ALMA data of the circumbinary disks with the dozen ‘Tatooine’ planets that have been found with the Kepler space telescope. To their surprise, the team found that the degree to which binary stars and their circumbinary disks are misaligned is strongly dependent on the orbital period of the host stars. The shorter the orbital period of the binary star, the more likely it is to host a disk in line with its orbit. However, binaries with periods longer than a month typically host misaligned disks [image credit: ALMA (ESO/NAOJ/NRAO), I. Czekala and G. Kennedy; NRAO/AUI/NSF, S. Dagnello]
- Czekala now wants to find out why there is such a strong correlation between disk (mis)alignment and the binary star orbital period. “We want to use existing and coming facilities like ALMA and the next generation Very Large Array to study disk structures at exquisite levels of precision,” he said, “and try to understand how warped or tilted disks affect the planet formation environment and how this might influence the population of planets that form within these disks.”
- “This research is a great example of how new discoveries build on previous observations,” said Joe Pesce, National Science Foundation Program Officer for NRAO and ALMA. “Discerning trends in the circumbinary disk population was only made possible by building on the foundation of archival observational programs undertaken by the ALMA community in previous cycles.”
- The astronomers published their results in The Astrophysical Journal. 48)
Figure 30: Two examples of aligned and misaligned protoplanetary disks around binary stars (circumbinary disks), observed with ALMA. Binary star orbits are added for clarity. Left: in star system HD 98800 B, the disk is misaligned with inner binary stars. The stars are orbiting each other (in this view, towards and away from us) in 315 days. Right: in star system AK Sco, the disk is in line with the orbit of its binary stars. The stars are orbiting each other in 13.6 days [image credit: ALMA (ESO/NAOJ/NRAO), I. Czekala and G. Kennedy; NRAO/AUI/NSF, S. Dagnello]
• March 5, 2020: An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) captured the very moment when an old star first starts to alter its environment. The star has ejected high-speed bipolar gas jets which are now colliding with the surrounding material; the age of the observed jet is estimated to be less than 60 years. These are key features to understand how the complex shapes of planetary nebulae are formed. 49)
- Sun-like stars evolve to puffed-up Red Giants in the final stage of their lives. Then, the star expels gas to form a remnant called a planetary nebula. There is a wide variety in the shapes of planetary nebulae; some are spherical, but others are bipolar or show complicated structures. Astronomers are interested in the origins of this variety, but the thick dust and gas expelled by an old star obscure the system and make it difficult to investigate the inner-workings of the process.
- To tackle this problem, a team of astronomers led by Daniel Tafoya in Chalmers University of Technology, Sweden, pointed ALMA at W43A, an old star system in the constellation Aquila, the Eagle.
- Thanks to ALMA’s high resolution, the team obtained a very detailed view of the space around W43A. “The most notable structures are its small bipolar jets,” says Tafoya, the lead author of the research paper published by the Astrophysical Journal Letters. The team found that the velocity of the jets is as high as 175 km per second, which is much higher than previous estimations. Based on this speed and the size of the jets, the team calculated the age of the jets to be less than a human life-span. 50)
- “Considering the youth of the jets compared to the overall lifetime of a star, it is safe to say we are witnessing the ‘exact moment’ that the jets have just started to shove through the surrounding gas,” explains Tafoya. “When the jets carve through the surrounding material in some 60 years, a single person can watch the progress in their life.”
- In fact, the ALMA image clearly maps the distribution of dusty clouds entrained by the jets, which is telltale evidence that it is impacting on the surroundings.
- The team assumes that this entrainment is the key to form a bipolar-shaped planetary nebula. In their scenario, the aged star originally ejects gas spherically and the core of the star loses its envelope. If the star has a companion, gas from the companion pours onto the core of the dying star, and a portion of this new gas forms the jets. Therefore, whether or not the old star has a companion is an important factor to determine the structure of the resulting planetary nebula.
Figure 31: ALMA image of the old star system W43A. The high velocity bipolar jets ejected from the central aged star are seen in blue, low velocity outflow is shown in green, and dusty clouds entrained by the jets are shown in orange (image credit: ALMA (ESO/NAOJ/NRAO), Tafoya et al.)
- “W43A is one of the peculiar so called ‘water fountain’ objects,” says Hiroshi Imai at Kagoshima University, Japan, a member of the team. “Some old stars show characteristic radio emissions from water molecules. We suppose that spots of these water emissions indicate the interface region between the jets and the surrounding material. We named them ‘water fountains,’ and it could be a sign that the central source is a binarity system launching a new jet.”
- “There are only 15 ‘water fountain’ objects identified to date, despite the fact that more than 100 billion stars are included in our Milky Way Galaxy,” explains José Francisco Gómez at Instituto de Astrofísica de Andalucía, Spain. “This is probably because the lifetime of the jets is quite short, so we are very lucky to see such rare objects.”
• February 20, 2020: An international team of astronomers used two of the most powerful radio telescopes in the world to create more than three hundred images of planet-forming disks around very young stars in the Orion Clouds. These images reveal new details about the birthplaces of planets and the earliest stages of star formation. 51)
- Most of the stars in the Universe are accompanied by planets. These planets are born in rings of dust and gas, called protoplanetary disks. Even very young stars are surrounded by these disks. Astronomers want to know exactly when these disks start to form, and what they look like. But young stars are very faint, and there are dense clouds of dust and gas surrounding them in stellar nurseries. Only highly sensitive radio telescope arrays can spot the tiny disks around these infant stars amidst the densely packed material in these clouds.
- For this new research, astronomers pointed both the Atacama Large Millimeter/submillimeter Array (ALMA) and the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to a region in space where many stars are born: the Orion Molecular Clouds. This survey, called VLA/ALMA Nascent Disk and Multiplicity (VANDAM), is the largest survey of young stars and their disks to date.
- Very young stars, also called protostars, form in clouds of gas and dust in space. The first step in the formation of a star is when these dense clouds collapse due to gravity. As the cloud collapses, it begins to spin – forming a flattened disk around the protostar. Material from the disk continues to feed the star and make it grow. Eventually, the left-over material in the disk is expected to form planets.
- Many aspects about these first stages of star formation, and how the disk forms, are still unclear. But this new survey provides some missing clues as the VLA and ALMA peered through the dense clouds and observed hundreds of protostars and their disks in various stages of their formation.
Young planet-forming disks
- “This survey revealed the average mass and size of these very young protoplanetary disks,” said John Tobin of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, and leader of the survey team. “We can now compare them to older disks that have been studied intensively with ALMA as well.”
- What Tobin and his team found, is that very young disks can be similar in size, but are on average much more massive than older disks. “When a star grows, it eats away more and more material from the disk. This means that younger disks have a lot more raw material from which planets could form. Possibly bigger planets already start to form around very young stars.”
Four special protostars
- Among hundreds of survey images, four protostars looked different than the rest and caught the scientists’ attention. “These newborn stars looked very irregular and blobby,” said team member Nicole Karnath of the University of Toledo, Ohio (now at SOFIA Science Center). “We think that they are in one of the earliest stages of star formation and some may not even have formed into protostars yet.”
- It is special that the scientists found four of these objects. “We rarely find more than one such irregular object in one observation,” added Karnath, who used these four infant stars to propose a schematic pathway for the earliest stages of star formation. “We are not entirely sure how old they are, but they are probably younger than ten thousand years.”
- To be defined as a typical (class 0) protostar, stars should not only have a flattened rotating disk surrounding them, but also an outflow – spewing away material in opposite directions – that clears the dense cloud surrounding the stars and makes them optically visible. This outflow is important, because it prevents stars from spinning out of control while they grow. But when exactly these outflows start to happen, is an open question in astronomy.
- One of the infant stars in this study, called HOPS 404, has an outflow of only two kilometers (1.2 miles) per second (a typical protostar-outflow of 10-100 km/s or 6-62 miles/s). “It is a big puffy sun that is still gathering a lot of mass, but just started its outflow to lose angular momentum to be able to keep growing,” explained Karnath. “This is one of the smallest outflows that we have seen and it supports our theory of what the first step in forming a protostar looks like.”
Combining ALMA and VLA
- The exquisite resolution and sensitivity provided by both ALMA and the VLA were crucial to understand both the outer and inner regions of protostars and their disks in this survey. While ALMA can examine the dense dusty material around protostars in great detail, the images from the VLA made at longer wavelengths were essential to understand the inner structures of the youngest protostars at scales smaller than our solar system.
- “The combined use of ALMA and the VLA has given us the best of both worlds,” said Tobin. “Thanks to these telescopes, we start to understand how planet formation begins.”
- The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
- This research was presented in two papers:
a) ”The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. A Statistical Characterization of Class 0 and I Protostellar Disks,” by J. Tobin et al., The Astrophysical Journal, Volume 890, No 2, Published: 20 February 2020, URL: https://doi.org/10.3847/1538-4357/ab6f64
b) “Detection of Irregular, Sub-mm Opaque Structures in the Orion Molecular Clouds: Protostars within 10000 years of formation?,” by N. Karnath et al., The Astrophysical Journal, Volume 890, No 2, Published: 20 February 2020, https://doi.org/10.3847/1538-4357/ab659e
- The original press release was published by the National Radio Astronomy Observatory (NRAO), an ALMA partner on behalf of North America.
Figure 32: VANDAM survey: ALMA and the VLA observed more than 300 protostars and their young protoplanetary disks in Orion. This image shows a subset of stars, including a few binaries. The ALMA and VLA data compliment each other: ALMA sees the outer disk structure (visualized in blue), and the VLA observes the inner disks and star cores (orange), image credit: ALMA (ESO/NAOJ/NRAO), J. Tobin; NRAO/AUI/NSF, S. Dagnello
Figure 33: Observed protostars in Orion Molecular Clouds: This image shows the Orion Molecular Clouds, the target of the VANDAM survey. Yellow dots are the locations of the observed protostars on a blue background image made by Herschel. Side panels show nine young protostars imaged by ALMA (blue) and the VLA (orange) image credit: ALMA (ESO/NAOJ/NRAO), J. Tobin; NRAO/AUI/NSF, S. Dagnello; Herschel/ESA
Figure 34: Schematic showing the formation of protostars: This schematic shows a proposed pathway (top row) for the formation of protostars, based on four very young protostars (bottom row) observed by VLA (orange) and ALMA (blue). Step 1 represents the collapsing fragment of gas and dust. In step 2, an opaque region starts to form in the cloud. In step 3, a hydrostatic core starts to form due to an increase in pressure and temperature, surrounded by a disk-like structure and the beginning of an outflow. Step 4 depicts the formation of a class 0 protostar inside the opaque region, that may have a rotationally supported disk and more well-defined outflows. Step 5 is a typical class 0 protostar with outflows that have broken through the envelope (making it optically visible), an actively accreting, rotationally supported disk. In the bottom row, white contours are the protostar outflows as seen with ALMA (image credit: ALMA (ESO/NAOJ/NRAO), N. Karnath; NRAO/AUI/NSF, B. Saxton and S. Dagnello)
Figure 35: Star chart of constellation Orion and observed protostars: The Orion Molecular Clouds (blue, as seen with Herschel) are located in the constellation Orion. Red dots show the locations of the observed protostars in the VANDAM survey (image credit: IAU; Sky & Telescope magazine; NRAO/AUI/NSF, S. Dagnello; Herschel/ESA; ALMA (ESO/NAOJ/NRAO), J. Tobin)
• February 5, 2020: Like humans, stars change with age and ultimately die. For the Sun and stars like it, this change will take it through a phase where, having burned all the hydrogen in its core, it swells up into a large and bright red-giant star. Eventually, the dying Sun will lose its outer layers, leaving behind its core: a hot and dense star called a white dwarf. 52)
- “The star system HD101584 is special in the sense that this ‘death process’ was terminated prematurely and dramatically as a nearby low-mass companion star was engulfed by the giant,” said Hans Olofsson of the Chalmers University of Technology, Sweden, who led a recent study, published in Astronomy & Astrophysics, of this intriguing object. 53)
- Thanks to new observations with ALMA, complemented by data from the ESO-operated Atacama Pathfinder EXperiment (APEX), Olofsson and his team now know that what happened in the double-star system HD101584 was akin to a stellar fight. As the main star puffed up into a red giant, it grew large enough to swallow its lower-mass partner. In response, the smaller star spiralled in towards the giant’s core but didn’t collide with it. Rather, this maneuver triggered the larger star into an outburst, leaving its gas layers dramatically scattered and its core exposed.
- The team says the complex structure of the gas in the HD101584 nebula is due to the smaller star’s spiralling towards the red giant, as well as to the jets of gas that formed in this process. As a deadly blow to the already defeated gas layers, these jets blasted through the previously ejected material, forming the rings of gas and the bright bluish and reddish blobs seen in the nebula.
- A silver lining of a stellar fight is that it helps astronomers to better understand the final evolution of stars like the Sun. “Currently, we can describe the death processes common to many Sun-like stars, but we cannot explain why or exactly how they happen. HD101584 gives us important clues to solve this puzzle since it is currently in a short transitional phase between better studied evolutionary stages. With detailed images of the environment of HD101584 we can make the connection between the giant star it was before, and the stellar remnant it will soon become,” says co-author Sofia Ramstedt from Uppsala University, Sweden.
- Co-author Elizabeth Humphreys from ESO in Chile highlighted that ALMA and APEX, located in the country’s Atacama region, were crucial to enabling the team to probe “both the physics and chemistry in action” in the gas cloud. She added: “This stunning image of the circumstellar environment of HD101584 would not have been possible without the exquisite sensitivity and angular resolution provided by ALMA.”
- While current telescopes allow astronomers to study the gas around the binary, the two stars at the center of the complex nebula are too close together and too far away to be resolved. ESO’s Extremely Large Telescope, under construction in Chile’s Atacama Desert, “will provide information on the ‘heart’ of the object,” says Olofsson, allowing astronomers a closer look at the fighting pair.
Figure 36: This new ALMA image shows the outcome of a stellar fight: a complex and stunning gas environment surrounding the binary HD101584. The colors represent speed, going from blue — gas moving the fastest towards us — to red — gas moving the fastest away from us. Jets, almost along the line of sight, propel the material in blue and red. The stars in the binary are located at the single bright dot at the center of the ring-like structure shown in green, which is moving with the same velocity as the system as a whole along the line of sight. Astronomers believe this ring has its origin in the material ejected as the lower mass star in the binary spiralled towards its red-giant partner (image credit: ALMA (ESO/NAOJ/NRAO), Olofsson et al. Acknowledgement: Robert Cumming)
• January 21, 2020: Phosphorus, present in our DNA and cell membranes, is an essential element for life as we know it. But how it arrived on the early Earth is something of a mystery. Astronomers have now traced the journey of phosphorus from star-forming regions to comets using the combined powers of ALMA and the European Space Agency’s probe Rosetta. Their research shows, for the first time, where molecules containing phosphorus form, how this element is carried in comets, and how a particular molecule may have played a crucial role in starting life on our planet. 54)
- “Life appeared on Earth about 4 billion years ago, but we still do not know the processes that made it possible,” says Víctor Rivilla, the lead author of a new study published today in the journal Monthly Notices of the Royal Astronomical Society. The new results from the Atacama Large Millimeter/Submillimeter Array(ALMA), in which the European Southern Observatory (ESO) is a partner, and from the ROSINA instrument on board Rosetta, show that phosphorus monoxide is a key piece in the origin-of-life puzzle. 55)
- With the power of ALMA, which allowed a detailed look into the star-forming region AFGL 5142, astronomers could pinpoint where phosphorus-bearing molecules, like phosphorus monoxide, form. New stars and planetary systems arise in cloud-like regions of gas and dust in between stars, making these interstellar clouds the ideal places to start the search for life’s building blocks.
- The ALMA observations showed that phosphorus-bearing molecules are created as massive stars are formed. Flows of gas from young massive stars open up cavities in interstellar clouds. Molecules containing phosphorus form on the cavity walls, through the combined action of shocks and radiation from the infant star. The astronomers have also shown that phosphorus monoxide is the most abundant phosphorus-bearing molecule in the cavity walls.
- After searching for this molecule in star-forming regions with ALMA, the European team moved on to a Solar System object: the now-famous comet 67P/Churyumov–Gerasimenko. The idea was to follow the trail of these phosphorus-bearing compounds. If the cavity walls collapse to form a star, particularly a less-massive one like the Sun, phosphorus monoxide can freeze out and get trapped in the icy dust grains that remain around the new star. Even before the star is fully formed, those dust grains come together to form pebbles, rocks and ultimately comets, which become transporters of phosphorus monoxide.
- ROSINA, which stands for Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, collected data from 67P for two years as Rosetta orbited the comet. Astronomers had found hints of phosphorus in the ROSINA data before, but they did not know what molecule had carried it there. Kathrin Altwegg, the Principal Investigator for Rosina and an author in the new study, got a clue about what this molecule could be after being approached at a conference by an astronomer studying star-forming regions with ALMA: “She said that phosphorus monoxide would be a very likely candidate, so I went back to our data and there it was!”
- This first sighting of phosphorus monoxide on a comet helps astronomers draw a connection between star-forming regions, where the molecule is created, all the way to Earth.
- “The combination of the ALMA and ROSINA data has revealed a sort of chemical thread during the whole process of star formation, in which phosphorus monoxide plays the dominant role,” says Rivilla, who is a researcher at the Arcetri Astrophysical Observatory of INAF, Italy’s National Institute for Astrophysics.
- “Phosphorus is essential for life as we know it,” adds Altwegg. “As comets most probably delivered large amounts of organic compounds to the Earth, the phosphorus monoxide found in comet 67P may strengthen the link between comets and life on Earth.”
- This intriguing journey could be documented because of the collaborative efforts between astronomers. “The detection of phosphorus monoxide was clearly thanks to an interdisciplinary exchange between telescopes on Earth and instruments in space,” says Altwegg.
- Leonardo Testi, ESO astronomer and ALMA European Operations Manager, concludes: “Understanding our cosmic origins, including how common the chemical conditions favorable for the emergence of life are, is a major topic of modern astrophysics. While ESO and ALMA focus on the observations of molecules in distant young planetary systems, the direct exploration of the chemical inventory within our Solar System is made possible by ESA missions, like Rosetta. The synergy between world leading ground-based and space facilities, through the collaboration between ESO and ESA, is a powerful asset for European researchers and enables transformational discoveries like the one reported in this paper.”
Figure 37: This ALMA image shows a detailed view of the star-forming region AFGL 5142. A bright, massive star in its infancy is visible at the center of the image. The flows of gas from this star have opened up a cavity in the region, and it is in the walls of this cavity (shown in color), that phosphorus-bearing molecules like phosphorus monoxide are formed. The different colors represent material moving at different speeds (image credit: ALMA (ESO/NAOJ/NRAO), Rivilla et al.)
Figure 38: This infographic shows the key results from a study that has revealed the interstellar thread of phosphorus, one of life’s building blocks. Thanks to ALMA, astronomers could pinpoint where phosphorus-bearing molecules form in star-forming regions like AFGL 5142. The background of this infographic shows a part of the night sky in the constellation of Auriga, where the star-forming region AFGL 5142 is located. The ALMA image of this object is on the top left of the infographic, and one of the locations where the team found phosphorus-bearing molecules is indicated by a circle. The most common phosphorus-bearing molecule in AFGL 5142 is phosphorus monoxide, represented in orange and red in the diagram on the bottom left. Another molecule found was phosphorus nitride, represented in orange and blue. -Using data from the ROSINA instrument onboard ESA’s Rosetta, astronomers also found phosphorus monoxide on comet 67P/Churyumov–Gerasimenko, shown on the bottom right. This first sighting of phosphorus monoxide on a comet helps astronomers draw a connection between star-forming regions, where the molecule is created, all the way to Earth, where it played a crucial role in starting life (image credit: ALMA (ESO/NAOJ/NRAO), Rivilla et al.; ESO/L. Calçada; ESA/Rosetta/NAVCAM; Mario Weigand, www.SkyTrip.de)
Figure 39: Mosaic of comet 67P/Churyumov–Gerasimenko, created using images taken on 10 September 2014 when ESA’s Rosetta spacecraft was 27.8 km from the comet (image credit: ESA/Rosetta/NAVCAM)
Figure 40: This wide-field view shows the region of the sky, in the constellation of Auriga, where the star-forming region AFGL 5142 is located. This view was created from images forming part of the Digitized Sky Survey 2 (image credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin)
Figure 41: This chart shows the location of the star-forming region AFGL 5142, recently observed with ALMA, in the constellation of Auriga. The map shows most of the stars visible to the unaided eye under good conditions, and AFGL 5142 itself is highlighted with a red circle on the image (image credit: ESO, IAU and Sky & Telescope)
• December 11, 2019: Astronomers using ALMA (Atacama Large Millimeter/submillimeter Array), have spotted the light of a massive galaxy seen only 970 million years after the Big Bang. This galaxy, called MAMBO-9, is the most distant dusty star-forming galaxy that has ever been observed without the help of a gravitational lens. 56)
- Dusty star-forming galaxies are the most intense stellar nurseries in the universe. They form stars at a rate up to a few thousand times the mass of the Sun per year (the star-forming rate of our Milky Way is just three solar masses per year) and they contain massive amounts of gas and dust. Such monster galaxies are not expected to have formed early in the history of the universe, but astronomers have already discovered several of them as seen when the cosmos was less than a billion years old. One of them is galaxy SPT0311-58, which ALMA observed in 2018.
- Because of their extreme behavior, astronomers think that these dusty galaxies play an important role in the evolution of the universe. But finding them is easier said than done. “These galaxies tend to hide in plain sight,” said Caitlin Casey of the University of Texas at Austin and lead author of a study published in The Astrophysical Journal. “We know they are out there, but they are not easy to find because their starlight is hidden in clouds of dust.” 57)
- MAMBO-9’s light was already detected ten years ago by co-author Manuel Aravena, using the Max-Planck Millimeter BOlometer (MAMBO) instrument on the IRAM 30-meter telescope in Spain and the Plateau de Bure Interferometer in France. But these observations were not sensitive enough to reveal the distance of the galaxy. “We were in doubt if it was real, because we couldn’t find it with other telescopes. But if it was real, it had to be very far away,” says Aravena, who was at that time a PhD student in Germany and is currently working for the Universidad Diego Portales in Chile.
- Thanks to ALMA’s sensitivity, Casey and her team have now been able to determine the distance of MAMBO-9. “We found the galaxy in a new ALMA survey specifically designed to identify dusty star-forming galaxies in the early universe,” said Casey. “And what is special about this observation, is that this is the most distant dusty galaxy we have ever seen in an unobstructed way.”
Figure 42: ALMA radio image of the dusty star-forming galaxy called MAMBO-9. The galaxy consists of two parts, and it is in the process of merging (image credit: ALMA (ESO/NAOJ/NRAO), C. M. Casey et al.; NRAO/AUI/NSF, B. Saxton)
- The light of distant galaxies is often obstructed by other galaxies closer to us. These galaxies in front work as a gravitational lens: they bend the light from the more distant galaxy. This lensing effect makes it easier for telescopes to spot distant objects (this is how ALMA could see galaxy SPT0311-58). But it also distorts the image of the object, making it harder to make out the details.
- In this study, the astronomers saw MAMBO-9 directly, without a lens, and this allowed them to measure its mass. “The total mass of gas and dust in the galaxy is enormous: ten times more than all the stars in the Milky Way. This means that it has yet to build most of its stars,” Casey explained. The galaxy consists of two parts, and it is in the process of merging.
- Casey hopes to find more distant dusty galaxies in the ALMA survey, which will give insight into how common they are, how these massive galaxies formed so early in the universe, and why they are so dusty. “Dust is normally a by-product of dying stars,” she said. “We expect one hundred times more stars than dust. But MAMBO-9 has not produced that many stars yet and we want to find out how dust can form so fast after the Big Bang.”
- “Observations with new and more capable technology can produce unexpected findings like MAMBO-9,” said Joe Pesce, National Science Foundation Program Officer for NRAO and ALMA. “While it is challenging to explain such a massive galaxy so early in the history of the universe, discoveries like this allow astronomers to develop an improved understanding of, and ask ever more questions about, the universe.”
Figure 43: Artist impression of what MAMBO-9 would look like in visible light. The galaxy is very dusty and it has yet to build most of its stars (image credit: NRAO/AUI/NSF, B. Saxton)
- The light from MAMBO-9 travelled about 13 billion years to reach ALMA’s antennas (the universe is approximately 13.8 billion years old today). That means that we can see what the galaxy looked like in the past (Watch this video to learn how ALMA works as a time-machine). Today, the galaxy would probably be even bigger, containing one hundred times more stars than the Milky Way, residing in a massive galaxy cluster.
- The National Radio Astronomy Observatory is a facility of the National Science Foundation (NSF), operated under cooperative agreement by Associated Universities, Inc.
• November 14, 2019: Two peacock-shaped gas clouds were revealed in the Large Magellanic Cloud (LMC) by observations with ALMA. A team of astronomers found several massive baby stars in the complex filamentary clouds, which agrees well with computer simulations of giant collisions of gas clouds. The researchers interpret this to mean that the filaments and young stars are telltale evidence of violent interactions between the LMC and the SMC (Small Magellanic Cloud) 200 million years ago. 58) 59)
- Astronomers know that stars are formed in collapsing clouds in space. However, the formation processes of giant stars, 10 times or more massive than the Sun, are not well understood because it is difficult to pack such a large amount of material into a small region. Some researchers suggest that interactions between galaxies provide a perfect environment for massive star formation. Due to the colossal gravity, clouds in the galaxies are stirred, stretched, and often collide with each other. A huge amount of gas is compressed in an unusually small area, which could form the seeds of massive stars.
- A research team used ALMA to study the structure of dense gas in N159, a bustling star formation region in the LMC. Thanks to ALMA’s high resolution, the team obtained a very detailed map of the clouds in two sub-regions, N159E-Papillon Nebula and N159W South.
- Interestingly, the cloud structures in the two regions look very similar: fan-shaped filaments of gas extending to the north with the pivots in the southernmost points. The ALMA observations also found several massive baby stars in the filaments in the two regions.
- “It is unnatural that in two regions separated by 150 light-years, clouds with such similar shapes were formed and that the ages of the baby stars are similar in two regions separated 150 light years,” says Kazuki Tokuda, a researcher at Osaka Prefecture University and the National Astronomical Observatory of Japan. “There must be a common cause of these features. Interaction between the LMC and SMC is a good candidate.”
- In 2017, Yasuo Fukui, a professor at Nagoya University and his team revealed the motion of hydrogen gas in the LMC and found that a gaseous component right next to N159 has a different velocity than the rest of the clouds. They suggested a hypothesis that the starburst is caused by a massive flow of gas from the SMC to the LMC, and that this flow originated from a close encounter between the two galaxies 200 million years ago.
- The pair of the peacock-shaped clouds in the two regions revealed by ALMA fits nicely with this hypothesis. Computer simulations show that many filamentary structures are formed in a short time scale after a collision of two clouds, which also backs this idea.
- “For the first time, we uncovered the link between massive star formation and galaxy interactions in very sharp detail,” says Fukui, the lead author of one of the research papers. “This is an important step in understanding the formation process of massive star clusters in which galaxy interactions have a big impact.”
Figure 44: ALMA images of two molecular clouds N159E-Papillon Nebula (left) and N159W South (right). Red and green show the distribution of molecular gas in different velocities seen in the emission from 13CO. The blue region in N159E-Papillon Nebula shows the ionized hydrogen gas observed with the Hubble Space Telescope. The blue part in N159W South shows the emission from dust particles obtained with ALMA [image credit: ALMA (ESO/NAOJ/NRAO)/Fukui et al./Tokuda et al./NASA-ESA Hubble Space Telescope]
• October 15, 2019: At the center of a galaxy called NGC 1068, a supermassive black hole hides within a thick doughnut-shaped cloud of dust and gas. When astronomers used ALMA ( Atacama Large Millimeter/submillimeter Array) to study this cloud in more detail, they made an unexpected discovery that could explain why supermassive black holes grew so rapidly in the early Universe. 60)
Figure 45: Artist's impression of the heart of galaxy NGC 1068, which harbors an actively feeding supermassive black hole, hidden within a thick doughnut-shaped cloud of dust and gas. ALMA discovered two counter-rotating flows of gas around the black hole. The colors in this image represent the motion of the gas: blue is material moving toward us, red is moving away (image credit: NRAO/AUI/NSF, S. Dagnello)
- “Thanks to the spectacular resolution of ALMA, we measured the movement of gas in the inner orbits around the black hole,” explains Violette Impellizzeri of the National Radio Astronomy Observatory (NRAO), working at ALMA in Chile and lead author on a paper published in the Astrophysical Journal. “Surprisingly, we found two disks of gas rotating in opposite directions.” 61)
- Supermassive black holes already existed when the Universe was young, just a billion years after the Big Bang. But how these extreme objects, whose masses are up to billions of times the mass of the Sun, had time to grow so fast, is an outstanding question among astronomers. This new ALMA discovery could provide a clue. “Counter-rotating gas streams are unstable, which means that clouds fall into the black hole faster than they do in a disk with a single rotation direction,” said Impellizzeri. “This could be a way in which a black hole can grow rapidly.”
- NGC 1068 (also known as Messier 77) is a spiral galaxy approximately 47 million light-years from Earth in the direction of the constellation Cetus. At its center is an active galactic nucleus, a supermassive black hole that is actively feeding itself from a thin, rotating disk of gas and dust, also known as an accretion disk.
Figure 46: ALMA image showing two disks of gas moving in opposite directions around the black hole in galaxy NGC 1068. The colors in this image represent the motion of the gas: blue is material moving toward us, red is moving away. The white triangles are added to show the accelerated gas that is expelled from the inner disk – forming a thick, obscuring cloud around the black hole (image credit: ALMA (ESO/NAOJ/NRAO), V. Impellizzeri; NRAO/AUI/NSF, S. Dagnello)
- Previous ALMA observations revealed that the black hole is gulping down material and spewing out gas at incredibly high speeds. This gas that gets expelled from the accretion disk likely contributes to hiding the region around the black hole from optical telescopes.
- Impellizzeri and her team used ALMA’s superior zoom lens ability to observe the molecular gas around the black hole. Unexpectedly, they found two counter-rotating disks of gas. The inner disk spans 2-4 light-years and follows the rotation of the galaxy, whereas the outer disk (also known as the torus) spans 4-22 light-years and is rotating the opposite way.
- “We did not expect to see this, because gas falling into a black hole would normally spin around it in only one direction,” said Impellizzeri. “Something must have disturbed the flow because it is impossible for a part of the disk to start rotating backward all on its own.”
- Counter-rotation is not an unusual phenomenon in space. “We see it in galaxies, usually thousands of light-years away from their galactic centers,” explained co-author Jack Gallimore from Bucknell University in Lewisburg, Pennsylvania. “The counter-rotation always results from the collision or interaction between two galaxies. What makes this result remarkable is that we see it on a much smaller scale, tens of light-years instead of thousands from the central black hole.”
- The astronomers think that the backward flow in NGC 1068 might be caused by gas clouds that fell out of the host galaxy, or by a small passing galaxy on a counter-rotating orbit captured in the disk.
- At the moment, the outer disk appears to be in a stable orbit around the inner disk. “That will change when the outer disk begins to fall onto the inner disk, which may happen after a few orbits or a few hundred thousand years. The rotating streams of gas will collide and become unstable, and the disks will likely collapse in a luminous event as the molecular gas falls into the black hole. Unfortunately, we will not be there to witness the fireworks,” said Gallimore.
• October 4, 2019: The two baby stars were found in the [BHB2007] 11 system – the youngest member of a small stellar cluster in the Barnard 59 dark nebula, which is part of the clouds of interstellar dust called the Pipe nebula. Previous observations of this binary system showed the outer structure. Now, thanks to the high resolution of the ALMA (Atacama Large Millimeter/submillimeter Array) and an international team of astronomers led by scientists from the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, we can see the inner structure of this object. 62)
- “We see two compact sources that we interpret as circumstellar disks around the two young stars,” explains Felipe Alves from MPE who led the study. A circumstellar disk is the ring of dust and gas that surrounds a young star. The star accrete matter from the ring to grow bigger. “The size of each of these disks is similar to the asteroid belt in our Solar System and the separation between them is 28 times the distance between the Sun and the Earth,” notes Alves.
- The two circumstellar disks are surrounded by a bigger disk with a total mass of about 80 Jupiter masses, which displays a complex network of dust structures distributed in spiral shapes – the pretzel loops. “This is a really important result,” stresses Paola Caselli, managing director at MPE, head of the Centre of Astrochemical Studies and co-author of the study. “We have finally imaged the complex structure of young binary stars with their feeding filaments connecting them to the disk in which they were born. This provides important constraints for current models of star formation.”
- The baby stars accrete mass from the bigger disk in two stages. The first stage is when mass is transferred to the individual circumstellar disks in beautiful twirling loops, which is what the new ALMA image showed. The data analysis also revealed that the less-massive but brighter circumstellar disk — the one in the lower part of the image — accretes more material. In the second stage, the stars accrete mass from their circumstellar disks. “We expect this two-level accretion process to drive the dynamics of the binary system during its mass accretion phase,” adds Alves. “While the good agreement of these observations with theory is already very promising, we will need to study more young binary systems in detail to better understand how multiple stars form.”
- This research was presented in a paper published on 3 October 2019 in the journal Science. 63)
- The team is composed of F. O. Alves (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics, Garching, Germany), P. Caselli (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics, Germany), J. M. Girart (Institut de Ciències de l’Espai, Consejo Superior de Investigaciones Científicas, Spain and Institut d’Estudis Espacials de Catalunya, Spain), D. Segura-Cox (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics, Garching, Germany), G. A. P. Franco (Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Brazil), A. Schmiedeke (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics, Garching, Germany) and B. Zhao (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics, Garching, Germany).
Figure 47: ALMA captured this unprecedented image of two circumstellar disks, in which baby stars are growing, feeding with material from their surrounding birth disk. The complex network of dust structures distributed in spiral shapes remind of the loops of a pretzel. These observations shed new light on the earliest phases of the lives of stars and help astronomers determine the conditions in which binary stars are born (image credit: ALMA (ESO/NAOJ/NRAO), Alves et al.)
• September 30, 2019: Using the detailed eyes of the ALMA (Atacama Large Millimeter/submillimeter Array) and ESO’s VLT (Very Large Telescope), astronomers have mapped the intense tails of a cosmic jellyfish: a number of knotty streams of gas spewing outwards from a spiral galaxy named ESO 137-001. 64)
Figure 48: This celestial cnidarian is shown here in beautiful detail. The various elements making up this image were captured by different telescopes. The galaxy and its surroundings were imaged by the NASA/ESA Hubble Space Telescope; its tails, which trace streams of hydrogen and show up in hues of bright purple, by the MUSE instrument mounted on the VLT; and bright hotspots of carbon dioxide emission from within the system, which show up as flares of orange-red, were spotted by ALMA [image credit: ALMA (ESO/NAOJ/NRAO), P. Jachym (Czech Academy of Sciences) et al.]
- These tails are caused by a dramatic phenomenon known as ram-pressure stripping. The space between galaxies in a cluster is not empty, but full of material that acts like a viscous fluid. As a galaxy travels through this resistant environment, gas is stripped out of the galaxy to form a wake that creates beautiful, intricate systems such as that seen here around ESO 137-001 (which resides in the Norma galaxy cluster). The direction and position of the tail shed light on the way in which the galaxy is moving — with galaxies usually falling towards the center of the cluster itself.
- This image offers the first high-resolution map of the cold molecular gas lurking within a ram-pressure stripped system. ESO 137-001 is one of the nearest jellyfish galaxies to Earth, and is particularly interesting because its long, extended tails of gas contain features known as ‘fireballs’: bursts of star formation. The precise mechanisms governing how stars form within jellyfish tails are mysterious, and this map thus provides a new window onto the conditions needed for new stars to form in such intense, changeable environments.
- The ALMA array comprises 66 antennas, and is located on the Chajinator plateau in the Chilean Atacama Desert at an altitude of 5000 meters. ALMA observes the night sky from this remote location to unlock the secrets of how the Universe — and its weird and wonderful residents, ESO 137-001 included — formed and evolved, revealing more about our cosmic origins.
• September 16, 2019: Star clusters are formed by the condensation of molecular clouds, masses of cold, dense gas that are found in every galaxy. The physical properties of these clouds in our own galaxy and nearby galaxies have been known for a long time. But are they identical in distant galaxies that are more than 8 billion light-years away? For the first time, an international team led by the University of Geneva (UNIGE) has been able to detect molecular clouds in a Milky Way progenitor, thanks to the unprecedented spatial resolution achieved in such a distant galaxy. 65)
- These observations, published in Nature Astronomy, show that the distant clouds have a higher mass, density and internal turbulence than the clouds hosted in nearby galaxies and that they produce far more stars. The astronomers attribute these differences to the ambient interstellar conditions in distant galaxies, which are too extreme for the molecular clouds typical of nearby galaxies to survive. 66)
- Molecular clouds consist of dense, cold molecular hydrogen gas that swirls around at supersonic velocities, generating density fluctuations that condense and form stars. In nearby galaxies, such as the Milky Way, a molecular cloud produces between 10+3 and 10+6 stars. In far-off galaxies, however, located more than 8 billion light-years away, astronomers have observed gigantic star clusters containing up to 100 times more stars. Why is there such a difference?
Exceptional observation made possible using a cosmic magnifying glass
- To answer this question, the astronomers were able to make use of a natural telescope - the gravitational lens phenomenon - in combination with ALMA (Atacama Large Millimeter / Submillimeter Array), an interferometer made up of 50 millimetric radio antennas that reconstruct the entire image of a galaxy instantly.
- "Gravitational lenses are a natural telescope that produces a magnifying-glass effect when a massive object is aligned between the observer and the distant object," explains Miroslava Dessauges, a researcher in the Department of Astronomy in UNIGE's Faculty of Science and first author of the study.
- "With this effect, some parts of distant galaxies are stretched on the sky and can be studied at an unrivalled resolution of 90 light-years!" ALMA, meanwhile, can be employed to measure the level of carbon monoxide, which acts as a tracer of molecular hydrogen gas that constitutes the cold clouds.
- This resolution made it possible to characterize the molecular clouds individually in a distant galaxy, nicknamed the "Cosmic Snake", 8 billion light-years away. "It's the first time we've been able to pinpoint molecular clouds one from each other," says Daniel Schaerer, professor in UNIGE's Department of Astronomy.
Figure 49: Molecular clouds detected at the unprecedented resolution of 90 light-years in the Cosmic Snake, located more than 8 billion light-years away, a typical progenitor of our galaxy (left). Observed at resolutions 50,000 times better, each of these clouds resembles the very tormented gas of the Carina nebula located only 7500 light-years away, a veritable nursery of emerging stars (right) image credit: © UNIGE, Dessauges et NASA, ESA
- The astronomers were therefore able to compare the mass, size, density and internal turbulence of molecular clouds in nearby and distant galaxies. "It was thought that the clouds had the same properties in all galaxies at all times, continues the Geneva-based researcher, but our observations have demonstrated the opposite!"
Molecular clouds resistant to extreme environments
- These new observations revealed that the molecular clouds in distant galaxies had a mass, density and turbulence 10 to 100 times higher than those in nearby galaxies. "Such values had only been measured in clouds hosted in nearby interacting galaxies, which have interstellar medium conditions resembling those of distant galaxies," adds Miroslava Dessauges.
- The researchers could link the differences in the physical properties of the clouds with the galactic environments, which are more extreme and hostile in far-off galaxies than in closer galaxies.
- "A molecular cloud typically found in a nearby galaxy would instantly collapse and be destroyed in the interstellar medium of distant galaxies, hence its enhanced density and turbulence guarantee its survival and equilibrium," explains Miroslava Dessauges.
- "The characteristic mass of the molecular clouds in the Cosmic Snake appears to be in perfect agreement with the predictions of our scenario of fragmentation of turbulent galactic disks. As a result, this scenario can be put forward as the mechanism of formation of massive molecular clouds in distant galaxies," adds Lucio Mayer, a professor at the Centre for Physical and Cosmological Theory at the University of Zurich.
- The international team also discovered that the efficiency of star formation in the Cosmic Snake galaxy is particularly high, likely triggered by the highly supersonic internal turbulence of the clouds. "In nearby galaxies, a molecular cloud forms about 5% of its mass in stars. In distant galaxies, this number climbs to 30%," observes Daniel Schaerer.
- The astronomers will now study other distant galaxies in order to confirm their observational results obtained for the Cosmic Snake. Miroslava Dessauges says in conclusion: "We'll also push the resolution even further by taking advantage of the unique performance of the ALMA interferometer. In parallel, we need to understand in more detail the ability of molecular clouds in distant galaxies to form stars so efficiently."
• September 13, 2019: Astronomers using one of the most advanced radio telescopes (ALMA) have discovered a rare molecule in the dust and gas disc around a young star — and it may provide an answer to one of the conundrums facing astronomers. 67)
- The star, named HD 163296, is located 330 light years from Earth and formed over the last six million years.
- It is surrounded by a disc of dust and gas — a so-called protoplanetary disc. It is within these discs that young planets are born. Using a radio telescope in the Atacama Desert in Chile, researchers were able to detect an extremely faint signal showing the existence of a rare form of carbon monoxide — known as an isotopologue (13C17O).
- The detection has allowed an international collaboration of scientists, led by the University of Leeds, to measure the mass of the gas in the disc more accurately than ever before. The results show that disc is much heavier — or more 'massive' — than previously thought.
- Alice Booth, a PhD researcher at Leeds who led the study, said: "Our new observations showed there was between two and six times more mass hiding in the disc than previous observations could measure.
- "This is an important finding in terms of the birth of planetary systems in discs — if they contain more gas, then they have more building material to form more massive planets."
- The study — The first detection of 13C17O in a protoplanetary disk: a robust tracer of disk gas mass — was published (12/09/2019) in the Astrophysical Journal Letters. 68)
- The scientists' conclusions are well timed. Recent observations of protoplanetary discs have perplexed astronomers because they did not seem to contain enough gas and dust to create the planets observed.
- Dr John Ilee, a researcher at Leeds who was also involved in the study, added: "The disc-exoplanet mass discrepancy raises serious questions about how and when planets are formed. However, if other discs are hiding similar amounts of mass as HD 163296, then we may just have underestimated their masses until now."
- "We can measure disc masses by looking at how much light is given off by molecules like carbon monoxide. If the discs are sufficiently dense, then they can block the light given off by more common forms of carbon monoxide -- and that could result in scientists underestimating the mass of the gas present. - This study has used a technique to observe the much rarer 13C17O molecule — and that's allowed us to peer deep inside the disc and find a previously hidden reservoir of gas."
- The researchers made use of one of the most sophisticated radio telescopes in the world — the ALMA (Atacama Large Millimeter/submillimeter Array) — high in the Atacama Desert.
Figure 50: The inner red regions represent the dust in the disc, thought to be shaped into rings by forming planets. The wider blue region is the carbon monoxide (CO) gas in the disc. The inner green region shows the rarer 13C17O gas that the researchers have detected for the first time (image credit: ALMA (ESO/NAOJ/NRAO), Booth and colleagues, University of Leeds)
- ALMA is able to observe light that is invisible to the naked eye, allowing astronomers to view what is known as the 'cold universe' — those parts of space not visible using optical telescopes.
- Booth said: "Our work shows the amazing contribution that ALMA is making to our understanding of the Universe. It is helping build a more accurate picture of the physics leading to the formation of new planets. This of course then helps us understand how the Solar System and Earth came to be."
- The researchers are already planning the next steps in their work.
- Booth added: "We suspect that ALMA will allow us to observe this rare form of CO in many other discs. By doing that, we can more accurately measure their mass, and determine whether scientists have systematically been underestimating how much matter they contain."
• August 22, 2019: Swirling clouds, big colorful belts, giant storms. The beautiful and incredibly turbulent atmosphere of Jupiter has been showcased many times. But what is going on below the clouds? What is causing the many storms and eruptions that we see on the ‘surface’ of the planet? However, to study this, visible light is not enough. We need to study Jupiter using radio waves. 69) 70)
- New radio wave images made with the ALMA (Atacama Large Millimeter/submillimeter Array) observatory provide a unique view of Jupiter’s atmosphere down to fifty kilometers below the planet’s visible (ammonia) cloud deck.
- “ALMA enabled us to make a three-dimensional map of the distribution of ammonia gas below the clouds. And for the first time, we were able to study the atmosphere below the ammonia cloud layers after an energetic eruption on Jupiter,” said Imke de Pater of the University of California, Berkeley (EE. UU.).
- The atmosphere of giant Jupiter is made out of mostly hydrogen and helium, together with trace gases of methane, ammonia, hydrosulfide, and water. The top-most cloud layer is made up of ammonia ice. Below that is a layer of solid ammonia hydrosulfide particles, and deeper still, around 80 kilometers below the upper cloud deck, there likely is a layer of liquid water. The upper clouds form the distinctive brown belts and white zones seen from Earth.
- Many of the storms on Jupiter take place inside those belts. They can be compared to thunderstorms on Earth and are often associated with lightning events. Storms reveal themselves in visible light as small bright clouds, referred to as plumes. These plume eruptions can cause a major disruption of the belt, which can be visible for months or years.
- The ALMA images were taken a few days after amateur astronomers observed an eruption in Jupiter’s South Equatorial Belt in January 2017. A small bright white plume was visible first, and then a large-scale disruption in the belt was observed that lasted for weeks after the eruption.
- De Pater and her colleagues used ALMA to study the atmosphere below the plume and the disrupted belt at radio wavelengths and compared these to UV-visible light and infrared images made with other telescopes at approximately the same time.
- “Our ALMA observations are the first to show that high concentrations of ammonia gas are brought up during an energetic eruption,” said de Pater. “The combination of observations simultaneously at many different wavelengths enabled us to examine the eruption in detail. Which led us to confirm the current theory that energetic plumes are triggered by moist convection at the base of water clouds, which are located deep in the atmosphere. The plumes bring up ammonia gas from deep in the atmosphere to high altitudes, well above the main ammonia cloud deck,” she added.
Figure 51: Radio image of Jupiter made with ALMA. Bright bands indicate high temperatures and dark bands low temperatures. The dark bands correspond to the zones on Jupiter, which are often white at visible wavelengths. The bright bands correspond to the brown belts on the planet. This image contains over 10 hours of data, so fine details are smeared by the planet’s rotation (image credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello)
- “These ALMA maps at millimeter wavelengths complement the maps made with the National Science Foundation’s Very Large Array in centimeter wavelengths,” said Bryan Butler of the NRAO (National Radio Astronomy Observatory). “Both maps probe below the cloud layers seen at optical wavelengths and show ammonia-rich gases rising into and forming the upper cloud layers (zones), and ammonia-poor air sinking down (belts).”
- “The present results show superbly what can be achieved in planetary science when an object is studied with various observatories and at various wavelengths”. Explains Eric Villard, an ALMA astronomer part of the research team. “ALMA, with its unprecedented sensitivity and spectral resolution at radio wavelengths, worked together successfully with other major observatories around the world, to provide the data to allow a better understanding of the atmosphere of Jupiter.”
Figure 52: Flat map of Jupiter in radio waves with ALMA (top) and visible light with the Hubble Space Telescope (bottom). The eruption in the South Equatorial Belt is visible in both images (image credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/Hubble)
Figure 53: Spherical ALMA map of Jupiter showing the distribution of ammonia gas below Jupiter’s cloud deck (image credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello)