Discoveries

Discoveries

On October 3, 2011, ALMA unveiled a new view of the Antenna Galaxies as its first scientific image. Even though ALMA was still under construction and contained only 12 antennas, the image showed ALMA’s scientific potential, revealing an unprecedented perspective over the merging galaxies by exposing the cold dust and gas in its interstellar medium.

The Antennae Galaxies (also known as NGC 4038 and 4039) are a pair of distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus (The Crow). This view combines ALMA observations, made in two different wavelength ranges during the observatory’s early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope. The Hubble image is the sharpest view of this object ever taken and serves as the ultimate benchmark in terms of resolution. ALMA observes at much longer wavelengths which makes it much harder to obtain comparably sharp images. However, when the full ALMA array is completed its vision will be up to ten times sharper than Hubble. Most of the ALMA test observations used to create this image were made using only twelve antennas working together — fewer than will be used for the first science observations — and much closer together as well. Both of these factors make the new image just a taster of what is to come. As the observatory grows, the sharpness, efficiency, and quality of its observations will increase dramatically as more antennas become available and the array grows in size. This is nevertheless the best submillimeter-wavelength image ever taken of the Antennae Galaxies and opens a new window on the submillimeter Universe. While visible light — shown here mainly in blue — reveals the newborn stars in the galaxies, ALMA’s view shows us something that cannot be seen at those wavelengths: the clouds of dense cold gas from which new stars form. The ALMA observations — shown here in red, pink and yellow — were made at specific wavelengths of millimeter and submillimeter light (ALMA bands 3 and 7), tuned to detect carbon monoxide molecules in the otherwise invisible hydrogen clouds, where new stars are forming. Massive concentrations of gas are found not only in the hearts of the two galaxies but also in the chaotic region where they are colliding. Here, the total amount of gas is billions of times the mass of the Sun — a rich reservoir of material for future generations of stars. Observations like these will be vital in helping us understand how galaxy collisions can trigger the birth of new stars. This is just one example of how ALMA reveals parts of the Universe that cannot be seen with visible-light and infrared telescopes. Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope
Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope

Over the next decade, the astronomical community has published more than 2,500 papers using ALMA data covering a wide range of targets in the Cosmos. From the farthest forming galaxies to the moons of the Solar System, the ALMA observatory has helped astronomers make transformational science, modifying the boundaries of our understanding in search of our Cosmic Origins.

Observations with ALMA have been able to deepen our understanding of a variety of astronomical subjects. Here there are some examples:

Galaxy formation

In 2018, astronomers studied the formation of galaxies and used ALMA to detect the most distant oxygen molecules known. The discovery located 13.28 billion light-years away allowed the research team to determine that star formation started unexpectedly in that galaxy, as early as 250 million years after the Big Bang. For a period after the Big Bang, there was no oxygen in the Universe. Oxygen was created in stars and then released when the stars died. The detection of oxygen in MACS1149-JD1 indicates that an earlier generation of stars had already formed and expelled processed oxygen by the galaxy’s age, which is only about 500 million years after the Universe’s beginning.

This image shows the galaxy cluster MACS J1149.5+2223 taken with the NASA/ESA Hubble Space Telescope and the inset image is the galaxy MACS1149-JD1 located 13.28 billion light-years away observed with ALMA. Here, the oxygen distribution detected with ALMA is depicted in green. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.
Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.

In 2020, the Astrophysical Journal published an unprecedented view of gas and dust in a cosmological deep field. An international group of astronomers used ALMA to obtain an inventory of molecular gas and dust in distant galaxies at unprecedented depth in the iconic Hubble Ultra-Deep Field (H-UDF), one of the best-studied regions of the sky. It has been well established that stars form from the gravitational collapse of dense clouds of molecular gas. Estimating galaxies’ molecular gas content and its development over cosmic time is indispensable to characterize their evolution. Such a measurement was one of the three prime directives driving ALMA from its conception. A research team led the ALMA large program ASPECS (The ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field) with this goal in mind. This was the first approved extragalactic large program designed to make an unbiased, three-dimensional survey of the molecular gas content of galaxies in the best-studied extragalactic deep field, the H-UDF.

Star Formation

ALMA radio telescope has also deepened the understanding of star formation. In 2021, astronomers used ALMA to map the nearby Universe and reveal the diversity of star-forming galaxies. Stars are formed out of clouds of dust and gas called molecular clouds, or stellar nurseries. Each stellar nursery in the Universe can form thousands or even tens of thousands of new stars during its lifetime. Between 2013 and 2019, astronomers on the PHANGS— Physics at High Angular Resolution in Nearby GalaxieS— project conducted the first systematic survey of 100,000 stellar nurseries across 90 galaxies in the nearby Universe to get a better understanding of how they connect back to their parent galaxies. They found that stellar nurseries are very diverse in shape and size and very different from place to place, resulting in consequences on the stars being formed.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), scientists completed a census of nearly 100 galaxies in the nearby Universe, showcasing their behaviors and appearances. The scientists compared ALMA data to that of the Hubble Space Telescope, shown in composite here. The survey concluded that contrary to popular scientific opinion, stellar nurseries do not all look and act the same. In fact, as shown here, they are as different as the neighborhoods, cities, regions, and countries that make up our own world. Credit: ALMA (ESO/NAOJ/NRAO)/PHANGS, S. Dagnello (NRAO)
Credit: ALMA (ESO/NAOJ/NRAO)/PHANGS, S. Dagnello (NRAO)

Earlier, in March 2018, astronomers used ALMA and other telescopes to reveal the inner web of the stellar nurseries in the Orion Nebula. A stunning image of a web of filaments appearing in red combines data from ALMA, IRAM’s 30-meter telescope, and the HAWK instrument in the ESO’s Very Large Telescope. The red filaments are structures of cold gas, only visible to telescopes working in the millimeter wavelength range, such as ALMA. They are invisible at both optical and infrared light, making ALMA one of the only instruments available for astronomers to study them. This gas gives rise to newborn stars — it gradually collapses under the force of its own gravity until it is sufficiently compressed to form a protostar — the precursor to a star.

This spectacular and unusual image shows part of the famous Orion Nebula, a star formation region lying about 1350 light-years from Earth. It combines a mosaic of millimetre wavelength images from the Atacama Large Millimeter/submillimeter Array (ALMA) and the IRAM 30-metre telescope, shown in red, with a more familiar infrared view from the HAWK-I instrument on ESO’s Very Large Telescope, shown in blue. The group of bright blue-white stars at the left is the Trapezium Cluster — made up of hot young stars that are only a few million years old. Credit: ESO/H. Drass/ALMA (ESO/NAOJ/NRAO)/A. Hacar
Credit: ESO/H. Drass/ALMA (ESO/NAOJ/NRAO)/A. Hacar

Death of Stars

Three decades ago, astronomers spotted one of the brightest exploding stars in more than 400 years. The titanic supernova, called Supernova 1987A (SN 1987A), blazed with the power of 100 million suns for several months following its discovery on February 23, 1987.

To commemorate the 30th anniversary of SN 1987A, astronomers released new images and research based on work combining data from NASA’s Hubble Space Telescope and Chandra X-ray Observatory, as well as ALMA, to explore SN 1987A like never before, opening a new era for the legendary supernova.

Three decades ago, astronomers spotted one of the brightest exploding stars in more than 400 years. The titanic supernova, called Supernova 1987A (SN 1987A), blazed with the power of 100 million suns for several months following its discovery on Feb. 23, 1987.
Credit: NASA/ESA, ALMA (ESO/NAOJ/NRAO)

Not all stars become supernovas when dying. Some 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.

In 2020, astronomers used ALMA to observe a set of stellar winds around aging stars and explained the mesmerizing shapes of planetary nebulae. Contrary to common consensus, the team found that stellar winds are often not spherical but form like planetary nebulae. They concluded that interaction with an accompanying star or exoplanet shapes the stellar winds and the planetary nebulae. The findings were published in the prestigious magazine Science.

Planets

In 2014, ALMA extended its arms to achieve its highest angular resolution and observed HL Tau. The revolutionary image revealed planetary genesis like no other telescope could before, taking an enormous step forward in understanding how protoplanetary disks develop and how planets form. The image exceeded all expectations and revealed a series of concentric and bright rings, separated by gaps. This ALMA image provided the most unmistakable evidence for ongoing planet formation within a protoplanetary disk and that planets form faster than previously thought.

This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO)
Credit: ALMA (ESO/NAOJ/NRAO)

The astronomical community continued to push the study of planetary genesis with ALMA over the years, and in 2018 a global team of researchers published the results of a campaign providing unprecedented views of the birth of planets. Known as the Disk Substructures at High Angular Resolution Project (DSHARP), this Large Program yielded stunning, high-resolution images of 20 nearby protoplanetary disks. It provided astronomers new insights into the variety of features in disks and the speed with which planets can emerge. According to the researchers, the most compelling interpretation of these observations is that giant planets, likely similar in mass to Neptune or Saturn, form quickly, much faster than current theory would indicate. They also tend to form in the outer reaches of their solar systems at tremendous distances from their host stars.

Solar System

Closer to the Earth, ALMA has also observed a diversity of targets, allowing astronomers and scientists to study our cosmic neighborhood better.

In 2019, astronomers used ALMA observations to unveil the guts of Jupiter’s storms: 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? To study this, visible light is not enough. Researchers needed to study Jupiter using radio waves. A new set of radio wave images made with ALMA provided a unique view of Jupiter’s atmosphere down to fifty kilometers below the planet’s visible cloud deck.

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. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello
Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello

Other targets studied in the Solar System are asteroids, comets, moons, and other planets. ALMA has even helped NASA precisely locate Pluto, allowing its mission New Horizons to get an unprecedented view of the dwarf planet.

ALMA image of comet 46P/Wirtanen taken on December 2 as the comet approached Earth. The ALMA image shows the concentration and distribution of hydrogen cyanide (HCN) molecules near the center of the comet's coma. Credit: ALMA (ESO/NAOJ/NRAO); M. Cordiner, NASA/CUA
Credit: ALMA (ESO/NAOJ/NRAO); M. Cordiner, NASA/CUA
Series of 4 images of the surface of Europa taken with ALMA, enabling astronomers to create the first global thermal map of Jupiter’s icy moon. Credit: ALMA (ESO/NAOJ/NRAO), S. Trumbo et al.
Credit: ALMA (ESO/NAOJ/NRAO), S. Trumbo et al.
Composite image of Uranus’s atmosphere and rings at radio wavelengths, taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in December 2017. The image shows thermal emission, or heat, from the rings of Uranus for the first time, enabling scientists to determine their temperature is a frigid 77 K (-320 F). Dark bands in Uranus’s atmosphere at these wavelengths show the presence of radiolight-absorbing molecules, in particular hydrogen sulfide (H2S) gas, whereas bright regions like the north polar spot contain very few of these molecules. Credit: ALMA (ESO/NAOJ/NRAO); E. Molter and I. de Pater.
Credit: ALMA (ESO/NAOJ/NRAO); E. Molter and I. de Pater.

Black Holes

Last but not least, ALMA has joined a global collaboration of radio observatories (the Event Horizon Telescope – EHT) to form an Earth-size interferometer and allow astronomers to reveal the first image of a black hole. ALMA is the largest millimeter-wave telescope in the world and was critical in the collaboration. ALMA’s unprecedented capabilities ensured high-quality calibration of the data to each of the other telescopes in the array, resulting in the fantastic images from the EHT.

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the center of Messier 87 and its shadow. The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon. Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialized supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. Credit: EHT Collaboration
Credit: EHT Collaboration

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