Gas ‘Waterfalls’ Reveal Infant Planets around Young Star

Artist impression of gas flowing like a waterfall into a protoplanetary disk gap, which is most likely caused by an infant planet. Credit: NRAO/AUI/NSF, S. Dagnello. Hi-Res File - Screensize File

Scientists measured the motion of gas (arrows) in a protoplanetary disk in three directions: rotating around the star, towards or away from the star, and up- or downwards in the disk. The insert shows a close-up of where a planet in orbit around the star pushes the gas and dust aside, opening a gap. Credit: NRAO/AUI/NSF, B. Saxton.  Hi-Res File - Screensize File

A computer simulation showed that the patterns of gas flows are unique and are most likely caused by planets in three locations in the disk. Planets in orbit around the star push the gas and dust aside, opening gaps. The gas above the gaps collapses into it like a waterfall, causing a rotational flow of gas in the disk.Credit: ALMA (ESO/NAOJ/NRAO), J. Bae; NRAO/AUI/NSF, S. Dagnell.  Hi-Res File - Screensize File

This animation shows the computer simulation of how the gas flows in the disk as a result of three planets in formation. Credit: ALMA (ESO/NAOJ/NRAO), J. Bae; NRAO/AUI/NSF, S. Dagnello. Download Video

Star chart showing the location of the young star HD 163296, in the constellation Sagittarius. HD 163296 is located about 398 light-years away from our Solar System. Credit: IAU; Sky & Telescope magazine; NRAO/AUI/NSF, S. Dagnello. Hi-Res File - Screensize File

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ALMA witnesses planet formation in action

The birthplaces of planets are disks made out of gas and dust. Astronomers study these so-called protoplanetary disks to understand the processes of planet formation. Beautiful images of disks made with the Atacama Large Millimeter/submillimeter Array (ALMA) show distinct gaps and ring features in dust, which may be caused by infant planets.

To get more certainty that these gaps are actually caused by planets, and to get a more complete view of planet formation, scientists study the gas in the disks in addition to dust. 99 percent of a protoplanetary disk’s mass is gas, of which carbon monoxide (CO) gas is the brightest component, emitting at a very distinctive millimeter-wavelength light that ALMA can observe.

Last year, two teams of astronomers demonstrated a new planet-hunting technique using this gas. They measured the velocity of CO gas rotating in the disk around the young star HD 163296. Localized disturbances in the movements of the gas revealed three planet-like patterns in the disk.

In this new study, lead author Richard Teague from the University of Michigan and his team used new high-resolution ALMA data from the Disk Substructures at High Angular Resolution Project (DSHARP) to study the gas’s velocity in more detail. “With the high fidelity data from this program, we were able to measure the gas’s velocity in three directions instead of just one,” said Teague. “For the first time, we measured the motion of the gas rotating around the star, towards or away from the star, and up- or downwards in the disk.”

Unique gas flows

Teague and his colleagues saw the gas moving from the upper layers towards the middle of the disk at three different locations. “What most likely happens is that a planet in orbit around the star pushes the gas and dust aside, opening a gap,” Teague explained. “The gas above the gap then collapses into it like a waterfall, causing a rotational flow of gas in the disk.”

This is the best evidence to date that there are indeed planets being formed around HD 163296. But astronomers cannot say with one hundred percent certainty that the gas flows are caused by planets. For example, the star’s magnetic field could also cause disturbances in the gas. “Right now, only a direct observation of the planets could rule out the other options. But the patterns of these gas flows are unique and it is very likely that they can only be caused by planets,” said co-author Jaehan Bae of the Carnegie Institution for Science, who tested this theory with a computer simulation of the disk.

The location of the three predicted planets in this study correspond to the results from last year: they are likely located at 87, 140 and 237 AU. (An astronomical unit – AU – is the average distance from the Earth to the Sun.) The closest planet to HD 163296 is calculated to be half the mass of Jupiter, the middle planet is Jupiter-mass, and the farthest planet is twice as massive as Jupiter.

Planet atmospheres

Gas flows from the surface towards the midplane of the protoplanetary disk have been predicted by theoretical models to exist since the late ‘90s, but this is the first time that they have been observed. Not only can they be used to detect infant planets, they also shape our understanding of how gas giant planets obtain their atmospheres.

“Planets form in the middle layer of the disk, the so-called midplane. This is a cold place, shielded from radiation from the star,” Teague explained. “We think that the gaps caused by planets bring in warmer gas from the more chemically active outer layers of the disk, and that this gas will form the atmosphere of the planet.”

Teague and his team did not expect that they would be able to see this phenomenon. “The disk around HD 163296 is the brightest and biggest disk we can see with ALMA,” said Teague. “But it was a big surprise to actually see these gas flows so clearly. The disks appears to be much more dynamic than we thought.”

“This gives us a much more complete picture of planet formation than we ever dreamed,” said co-author Ted Bergin of the University of Michigan. “By characterizing these flows we can determine how planets like Jupiter are born and characterize their chemical composition at birth. We might be able to use this to trace the birth location of these planets, as they can move during formation.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Source: National Radio Astronomy Observatory (NRAO)/News

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Iris Nijman
Interim Public Information Officer for ALMA
alma-pr@nrao.edu

This research is presented in a paper titled: “Meridional flows in the disk around a young star,” by R. Teague, et al. in Nature. Doi: 10.1038/s41586-019-1642-0 The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (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) in Taiwan 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 by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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Stormy cluster weather could unleash black hole power and explain lack of cosmic cooling

Figure 1. The left hand panel shows an actual observation of the galaxy cluster MS 0735.6+7421, while on the right the background Hubble image has instead been overlaid with a mock observation of the jet (pink) and X-ray emission (blue) made from the simulation. Both images show cavities excavated by the lobe inflation surround by X-ray bright rims of dense gas (blue), which are filled by distorted jet material (pink). Image credit: Hubble and Chandra Image: NASA, ESA, CXC, STScI, and B. McNamara (University of Waterloo); Very Large Array Telescope Image: NRAO, and L. Birzan and team (Ohio University); Simulated Data: M. A. Bourne (University of Cambridge).

Figure 2. An artist’s impression of the jet launched by a supermassive black hole, which inflates lobes of very hot gas that are distorted by the cluster weather. Image credit: Institute of Astronomy, University of Cambridge.

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“Weather” in clusters of galaxies may explain a longstanding puzzle, according to a team of researchers at the University of Cambridge. The scientists used sophisticated simulations to show how powerful jets from supermassive black holes are disrupted by the motion of hot gas and galaxies, preventing gas from cooling, which could otherwise form stars. The team publish their work in the journal Monthly Notices of the Royal Astronomical Society.

 Typical clusters of galaxies have several thousand member galaxies, which can be very different to our own Milky Way and vary in size and shape. These systems are embedded in very hot gas known as the intracluster medium (ICM), all of which live in an unseen halo of so-called ‘dark matter’.

A large number of galaxies have supermassive black holes in their centres, and these often have high speed jets of material stretching over thousands of light years that can inflate very hot lobes in the ICM.

 The researchers, based at the Kavli Institute for Cosmology and Institute of Astronomy performed state-of-the-art simulations looking at the jet lobes in fine detail and the X-rays emitted as a result. The model captures the birth and cosmological evolution of the galaxy cluster, and allowed the scientists to investigate with unprecedented realism how the jets and lobes they inflate interact with a dynamic ICM.

They found that the mock X-ray observations of the simulated cluster revealed the so-called “X-ray cavities” and “X-ray bright rims” generated by supermassive black hole-driven jets, which itself is distorted by motions in the cluster remarkably resemble those found in observations of real galaxy clusters.

 Dr Martin Bourne of the Institute of Astronomy in Cambridge led the team. He commented: “We have developed new computational techniques, which harness the latest high-performance computing technology, to model for the first time the jet lobes with more than a million elements in fully realistic clusters. This allows us to place the physical processes that drive the liberation of the jet energy under the microscope.”

 As galaxies move around in the cluster, the simulation shows they create a kind of ‘weather’, moving, deforming and destroying the hot lobes of gas found at the end of the black hole jets. The jet lobes are enormously powerful and if disrupted, deliver vast amounts of energy to the ICM.

The Cambridge team believe that this cluster weather disruption mechanism may solve an enduring problem: understanding why ICM gas does not cool and form stars in the cluster centre. This so-called “cooling flow” puzzle has plagued astrophysicists for more than 25 years.

 The simulations performed provide a tantalizing new solution that could solve this problem. Dr Bourne commented: “The combination of the huge energies pumped into the jet lobes by the supermassive black hole and the ability of cluster weather to disrupt the lobes and redistribute this energy to the ICM provides a simple and yet elegant mechanism to solve the cooling flow problem.”

A series of next generation X-ray space telescopes will launch into orbit over the next decade. These advanced instruments should help settle the debate – and if intergalactic weather really does stop the birth of stars.

Source: Kavli Institute for Cosmology, Cambridge (KICC)/News

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Notes

The simulations have been performed on the STFC DiRAC HPC facilities which are part of the National e-Infrastructure. The research was funded by European Research Council, STFC and the Kavli Foundation. This work has been accepted by Monthly Notices of the Royal Astronomical Society: “AGN jet feedback on a moving mesh: lobe energetics and X-ray properties in a realistic cluster environment” by Martin A. Bourne, Debora Sijacki and Ewald Puchwein.

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Science Contact

Dr Martin Bourne
Kavli Institute for Cosmology, Cambridge
Institute of Astronomy
Cambridge
Mob: +44 (0)7557380858
mabourne@ast.cam.ac.uk

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Going Against the Flow Around a Supermassive Black Hole

Artist 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. Credit: NRAO/AUI/NSF, S. Dagnello. Hi-Res File/Screensize File

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. Credit: ALMA (ESO/NAOJ/NRAO), V. Impellizzeri; NRAO/AUI/NSF, S. Dagnello. Hi-Res File/Screensize File

Star chart showing the location of NGC 1068 (also known as Messier 77), a spiral galaxy approximately 47 million light-years from Earth in the direction of the constellation Cetus. Credit: IAU; Sky & Telescope magazine; NRAO/AUI/NSF, S. Dagnello. Hi-Res File/Screensize File

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 the Atacama Large Millimeter/submillimeter Array (ALMA)

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.

“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.”

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 in such a relatively short timespan, 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.

Previous ALMA observations revealed that the black hole is not only gulping down material, but also spewing out gas at incredibly high speeds – up to 500 kilometers per second (more than one million miles per hour). 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.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Source: National Radio Astronomy Observatory (NRAO)/News

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Contact:

Iris Nijman
Interim Public Information Officer for ALMA
alma-pr@nrao.edu

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Reference:

“Counter-Rotation and High Velocity Outflow in the Parsec-Scale Molecular Torus of NGC 1068,” C. M. Violette Impellizzeri et. al., the Astrophysical Journal. DOI: 10.3847/2041-8213/ab3c64

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is 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 by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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Astronomers use giant galaxy cluster to magnify X-ray emissions of an early-forming galaxy

False color and X-ray images of the giant arc in SPT-CLJ2344-4243. The X-ray emitting giant arc is shown relative to the center of the foreground lensing galaxy cluster in a false color image at optical wavelengths. The inset shows Chandra X-ray 0.5–7 keV (left) and Hubble optical (right) images of the giant arc at a scale 1.5 times larger.

A team of astronomers, including Professor Keren Sharon from the University of Michigan, have utilized a massive cluster of galaxies in order to look back in time to the first generation of galaxies. The work of Sharon and her coauthors, led by Matthew Bayliss, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research, was published recently in Nature Astronomy.

An experiment of gravitational lensing

In previous studies, strong gravitational lensing by galaxy clusters was leveraged to observe faint galaxies at optical and infrared wavelengths. However, this is the first time gravitational lensing has been used to peer into distant star formation in the X-ray.

While conducting their research, the astronomers detected an infant galaxy, about 1/10,000 the size of the Milky Way, in its first high-energy stage of star formation. According to Sharon and her colleagues, the detection of this distant galaxy supports the idea that scientists can use galaxy clusters to observe phenomena dating back to the universe’s early history – in this case, nearly 9.4 billion years ago.

Galaxy clusters are the most massive objects in the universe. Because they are so large and composed of many galaxies all bound together by gravity, their gravitational pull is often so strong that it can bend space-time. When this happens, light may no longer move in straight lines as its path is warped by the gravitational pull of the cluster. As a result, the light from background objects is magnified. When this phenomena is used to astronomers’ advantage, it is called gravitational lensing.

Galaxy clusters are the most massive gravitationally bound objects in the Universe, composed of dark matter, hot gas, hundreds of galaxies. Because they are so massive, their gravity bends space-time, an effect predicted by Einstein’s general relativity. When this happens, light may no longer move in straight lines as its path follows the warped space-time. As a result, the image of background objects appears distorted and magnified. When this phenomena is used to astronomers’ advantage, it is called gravitational lensing.

“We have observed that the Phoenix cluster is causing lensing of several background sources, magnifying them and creating multiple images,” said Sharon. “I can take those observations and use them to solve for how much mass there is in this intervening object and determine the degree of magnification.”

Gravitational lensing essentially allows astronomers to use galaxy clusters as enormous magnifying glasses. If they are able to approximate the mass of a cluster, they can estimate the gravitational effects it may have on background light sources. For instance, the light from an object positioned behind the cluster would travel directly towards the cluster before bending around it and continuing towards the observer, appearing as distorted, magnified images of the object. This helps astronomers study galaxies that would otherwise be too faint for present-day telescopes.

Sourcing the X-rays

While studying gravitationally-lensed faint galaxies is now routine, faint X-ray sources behind galaxy clusters pose an additional challenge. The cores of galaxy clusters are filled with hot gas, which emits brightly in the X-ray. The X-ray light of the background source, although magnified, can be lost in the X-ray light of the foreground cluster.

While examining X-ray data of the Phoenix cluster, Dr. Bayliss realized that there was X-ray emission originating from one of the gravitationally-lensed background galaxies that appeared as a point source.

“This radiation is likely coming not from something that is very X-ray luminous, but from a stellar object or X-ray binary,” said Sharon. “This is very hard to see at such large distances and is only visible in this case because it is being magnified by the Phoenix cluster at a factor of 60. This is the farthest away it’s ever been seen.”

Isolating the background object

In order to achieve a better understanding of the identified X-ray emissions, the team tested whether they could isolate the fainter X-rays coming from the background object. Using data taken by NASA’s Chandra X-ray Observatory, the Hubble Space Telescope and the Magellan telescope in Chile, the team developed a model to precisely measure the X-ray emissions from the Phoenix cluster and subtract it from the data. What was left were the lensed emissions that they were able to trace back to a tiny dwarf galaxy, originating approximately 9.4 billion years ago.

The researchers further examined the the X-ray, optical, and infra-red emission coming from this galaxy and were able to measure its physical conditions, such as age, metallicity (the fraction of heavy elements), star formation rate, and mass. The gravitational lensing analysis, led by Sharon, enabled the team to convert the observed measurements to the intrinsic ones one would have measured without lensing magnification. Because this galaxy has low mass and low metallicity, and because X-rays are typically produced during extreme events, the researchers conclude that this galaxy may by similar to the first generation of galaxies formed in the very early universe, and responsible for ionizing it.

“The universe’s first stars and galaxies had enough energetic photons to create larger and larger spheres for ionized materials. After that epoch, light was free to travel through the universe,” said Sharon. “It’s interesting to find galaxies that are analogs of those first galaxies in an epoch where we can see them.”

by Nicholle Cardinal

Source: LSA/Astronomy - University of Michigan/News

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More Information:

• Professor Keren Sharon
• Link to Published Study
• Link to MIT Press Release

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Feeding a Baby Star Through a Whirlpool in Space

(Top) Optical image of the jet in the HH 111 protostellar system taken by the Hubble Space Telescope (Reipurth et al. 1999). (Bottom left) Accretion disk detected with ALMA in dust continuum emission at 850 micron. (Bottom middle) The disk turned (de-projected) to be face-on, showing a pair of faint spirals. (Bottom right) Annularly averaged continuum emission is subtracted to highlight the faint spirals in the disk. Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al. Scientific Paper

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) detected a pair of spiral arms in an accretion disk around a baby star. Interestingly, these spiral density enhancements make the disk appear like a “space whirlpool.” The finding supports current theories of accretion disk feeding process, and potentially brings critical insights into the processes of grain growth and settling that are important to planet formation. These results appear in an article in Nature Astronomy led by Chin-Fei Lee at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan).

“Thanks to the resolving power of ALMA, we finally detected a pair of spirals in a young accretion disk around a baby star. These spirals, long predicted in theory, play a crucial role in the transport of angular momentum. Which allows disk material to swirl towards the baby star”, says Lee with excitement. “Our detection of the spirals is an important milestone in understanding the feeding process of baby stars.”

Spirals detected in protoplanetary disks around somewhat older stars seem to be produced by interaction with unseen baby planets. Unlike those, the spirals here are induced by accretion of material from the surrounding molecular cloud onto the disk.

The protostar with its disk lies at the center of HH 111, a pair of supersonic jets emerging from a molecular cloud core located 1300 lightyears away in the constellation Orion. The protostar is about half a million years old, just one ten-thousandth the age of our Sun, and has a mass 50% greater than our Sun. A portion of the flow through the disk onto the budding star is diverted to form the spectacular jets. Previous observations with a resolution of 120 AU (An astronomical unit – AU – is the average distance from the Earth to the Sun) detected the accretion disk orbiting the protostar out to a radius of 160 AU. The new observations with ALMA have a resolution of 16 AU, almost eight times better. With this outstanding capability, astronomers were able to resolve the disk spatially. They detected a pair of spiral arms by the glow of thermal emission from dust particles concentrated there (Figure 1).

The team’s observations open up the exciting possibility of detecting spiral structures in the accretion disks around protostars through high-resolution and high-sensitivity imaging with ALMA, which allows studying accretion disk feeding processes in depth. Such observations also provide insight into accretion disks around other kinds of astrophysical objects, including the supermassive black holes found at the center of active galaxies. 

Source: Atacama Large Millimeter/submillimeter Array (ALMA)/Press Release

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Additional information

This research was presented in a paper “Spiral Structures in an Embedded Protostellar Disk Driven by Envelope Accretion,” by Lee et al. to appear in Nature Astronomy.

The team is composed of Chin-Fei Lee (ASIAA, Taiwan; National Taiwan University, Taiwan), Zhi-Yun Li (University of Virginia, USA), and Neal J. Turner (JPL/Caltech, USA).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of 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 National Science Council of Taiwan (NSC) 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 by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified

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Contact

Nicolás Lira
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Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
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Masaaki Hiramatsu
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Observatory
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Email: hiramatsu.masaaki@nao.ac.jp

Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
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Email: alma-pr@nrao.edu

Mariya Lyubenova
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Email: mlyubeno@eso.org

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A triple merger in the early Universe

The total brightness (contours), velocity along our line of sight (colors of top panel), and speed of random motions (colors of bottom panel) of  DEIMOS COSMOS 818760.

As part of the multinational ALPINE collaboration, scientists at the Kavli Institute have discovered a system of three galaxies merging together when the universe was only 1.3 billion years old.

The ALPINE program (ALMA Large Program to INvestigate CII at Early times) is an extensive project using the Atacama Large Millimetre Array (ALMA) to look at the ionized carbon emission (tracing regions that are actively forming stars) from 118 galaxies as they were ~1-1.5 billion years after the Big Bang. One of the primary goals is to characterize the dynamics of each galaxy in the sample, including how many are merging with other galaxies and how many feature regular rotating disks.

One of the galaxies in this sample (named DEIMOS COSMOS 818760), features three clumps of emission. From the way the clumps are distributed, how they are moving, and by comparing them with simulations, they are interpreted as three galaxies that are merging together in the early Universe. The two brightest sources are close together and show signs of interaction, while the third source is slightly weaker and more distant. The discovery of such complex interactions between galaxies in the early Universe provides previous information for understanding the early formation of galaxies and of their subsequent evolution.

Only a handful of triple mergers have been detected in the early universe, and further analysis of the ALPINE data is sure to reveal more.

The investigation of this galaxy was led by Gareth Jones, a postdoctoral research associate at the Kavli Institute, and the results were published in this week's issue of Monthly Notices of the Royal Astronomical Society: Letters - https://academic.oup.com/mnrasl/advance-article-abstract/doi/10.1093/mnrasl/slz154/5582601. This is the very first paper published by the ALPINE collaboration and it is opening a sequel of several other papers that will be published in the coming months presenting various other important results that provide new important information on the primeval stages of galaxy evolution.

The ALPINE project is led by Olivier Le Févre.

Source:  Kavli Institute for Cosmology, Cambridge (KICC)/News

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Saturn Surpasses Jupiter After Discovery of 20 New Moons

Figure 1: The discovery images for the newly found very distant prograde moon of Saturn. They were taken on the Subaru Telescope with about one hour between each image. The background stars and galaxies do not move, while the newly discovered Saturnian moon, highlighted with an orange bar, shows motion between the two images. (Photographs are courtesy of Scott Sheppard.)

Using the Subaru Telescope, a team led by Carnegie's Scott S. Sheppard has found 20 new moons orbiting Saturn. This brings the ringed planet's total number of moons to 82, surpassing Jupiter, which has 79. The discovery was announced on October 7, 2019, by the International Astronomical Union's Minor Planet Center.

Each of the newly discovered moons is about five kilometers, or three miles, in diameter. Seventeen of them orbit the planet backwards, or in a retrograde direction, meaning their movement is opposite of the planet's rotation around its axis. The other three moons orbit in the prograde—the same direction as Saturn rotates.

Two of the prograde moons are closer to the planet and take about two years to travel once around Saturn. The more-distant retrograde moons and one of the prograde moons each take more than three years to complete an orbit.

"Studying the orbits of these moons can reveal their origins, as well as information about the conditions surrounding Saturn at the time of its formation," Sheppard explained.

The outer moons of Saturn appear to be grouped into three different clusters in terms of the inclinations of the angles at which they are orbiting around the planet. Two of the newly discovered prograde moons fit into a group of outer moons with inclinations of about 46 degrees called the Inuit group, as they are named after Inuit mythology. These moons may have once comprised a larger moon that was broken apart in the distant past. Likewise, the newly announced retrograde moons have similar inclinations to other previously known retrograde Saturnian moons, indicating that they are also likely fragments from a once-larger parent moon that was broken apart. These retrograde moons are in the Norse group, with names coming from Norse mythology. One of the newly discovered retrograde moons is the farthest known moon around Saturn.

"This kind of grouping of outer moons is also seen around Jupiter, indicating violent collisions occurred between moons in the Saturnian system or with outside objects such as passing asteroids or comets," explained Sheppard.

The other newly found prograde moon has an inclination near 36 degrees, which is similar to the other known grouping of inner prograde moons around Saturn called the Gallic group. But this new moon orbits much farther away from Saturn than any of the other prograde moons, indicating it might have been pulled outwards over time or might not be associated with the more inner grouping of prograde moons.

If a significant amount of gas or dust were present when a larger moon broke apart and created these clusters of smaller moon fragments, there would have been strong frictional interactions between the smaller moons and the gas and dust, causing them to spiral into the planet.

"In the Solar System's youth, the Sun was surrounded by a rotating disk of gas and dust from which the planets were born. It is believed that a similar gas-and-dust disk surrounded Saturn during its formation," Sheppard said. "The fact that these newly discovered moons were able to continue orbiting Saturn after their parent moons broke apart indicates that these collisions occurred after the planet-formation process was mostly complete and the disks were no longer a factor."

Figure 2: An artist's conception of the 20 newly discovered moons orbiting Saturn. These discoveries bring the planet's total moon count to 82, surpassing Jupiter for the most in our Solar System. Studying these moons can reveal information about their formation and about the conditions around Saturn at the time. Illustration is courtesy of the Carnegie Institution for Science. (Illustration is courtesy of the Carnegie Institution for Science. Saturn image is courtesy of NASA/JPL-Caltech/Space Science Institute. Starry background courtesy of Paolo Sartorio/Shutterstock.)

The new moons were discovered using the Subaru Telescope. The observing team included Sheppard, David Jewitt of UCLA, and Jan Kleyna of the University of Hawaii.

"Using some of the largest telescopes in the world, we are now completing the inventory of small moons around the giant planets," says Scott Sheppard. "They play a crucial role in helping us determine how our Solar System's planets formed and evolved."

Last year, Sheppard discovered 12 new moons orbiting Jupiter and Carnegie hosted an online contest to name five of them.

"I was so thrilled with the amount of public engagement over the Jupiter moon-naming contest that we've decided to do another one to name these newly discovered Saturnian moons," Sheppard said. "This time, the moons must be named after giants from Norse, Gallic, or Inuit mythology." Contest details are available here.

Source: Subaru Telescope

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Links

• Saturn Surpasses Jupiter After Discovery of 20 New Moons (Press Releases from The Carnegie Institution for Science)
• More details about Saturn's moons (Dr. Scott S. Sheppard's website)

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Milky Way Raids Intergalactic 'Bank Accounts,' Hubble Study Finds

Artist’s Impression of Milky Way Inflows and Outlfows

Artist's Illustration: NASA, ESA, and D. Player (STScI )
Science: NASA, ESA, and A. Fox (STScI )

Audit of the Milky Way's gas flow rates reveals a mysterious surplus of inflowing gas.

Astronomers have discovered an unexplained surplus of gas flowing into our Milky Way after conducting a galaxy-wide audit of outflowing and inflowing gas. Rather than a gas equilibrium and "balanced books," 10 years of data from NASA's Hubble Space Telescope show there is more gas coming in than going out.

It is no secret that the Milky Way is frugal with its gas. The valuable raw material is recycled over billions of years—thrown out into the galactic halo via supernovas and violent stellar winds, and then used to form new generations of stars once it falls back to the galactic plane. The surplus of inflowing gas, however, was a surprise.

Hubble distinguished between outflowing and inflowing clouds using its sensitive Cosmic Origins Spectrograph (COS), which detects the movement of the invisible gas. As the gas moves away it appears redder, while gas falling back toward the Milky Way is bluer.

The source of the excess gas inflow remains a mystery. Astronomers theorize that the gas could be coming from the intergalactic medium, as well as the Milky Way raiding the gas "bank accounts" of its small satellite galaxies using its considerably greater gravitational pull.

Our Milky Way is a frugal galaxy. Supernovas and violent stellar winds blow gas out of the galactic disk, but that gas falls back onto the galaxy to form new generations of stars. In an ambitious effort to conduct a full accounting of this recycling process, astronomers were surprised to find a surplus of incoming gas.

"We expected to find the Milky Way's books balanced, with an equilibrium of gas inflow and outflow, but 10 years of Hubble ultraviolet data has shown there is more coming in than going out," said astronomer Andrew Fox of the Space Telescope Science Institute, Baltimore, Maryland, lead author of the study to be published in The Astrophysical Journal.

Fox said that, for now, the source of the excess inflowing gas remains a mystery.

One possible explanation is that new gas could be coming from the intergalactic medium. But Fox suspects the Milky Way is also raiding the gas "bank accounts" of its small satellite galaxies, using its considerably greater gravitational pull to siphon away their resources. Additionally, this survey, while galaxy-wide, looked only at cool gas, and hotter gas could play a role, too.

The new study reports the best measurements yet for how fast gas flows in and out of the Milky Way. Prior to this study, astronomers knew that the galactic gas reserves are replenished by inflow and depleted by outflow, but they did not know the relative amounts of gas coming in compared to going out. The balance between these two processes is important because it regulates the formation of new generations of stars and planets.

Astronomers accomplished this survey by collecting archival observations from Hubble’s Cosmic Origins Spectrograph (COS), which was installed on the telescope by astronauts in 2009 during its last servicing mission. Researchers combed through the Hubble archives, analyzing 200 past ultraviolet observations of the diffuse halo that surrounds the disk of our galaxy. The decade's worth of detailed ultraviolet data provided an unprecedented look at gas flow across the galaxy and allowed for the first galaxy-wide inventory. The gas clouds of the galactic halo are only detectable in ultraviolet light, and Hubble is specialized to collect detailed data about the ultraviolet universe.

"The original Hubble COS observations were taken to study the universe far beyond our galaxy, but we went back to them and analyzed the Milky Way gas in the foreground. It's a credit to the Hubble archive that we can use the same observations to study both the near and the more distant universe. Hubble's resolution allows us to simultaneously study local and remote celestial objects," noted Rongmon Bordoloi of North Carolina State University in Raleigh, North Carolina, a co-author on the paper.

Because the galaxy's gas clouds are invisible, Fox's team used light from background quasars to detect these clouds and their motion. Quasars, the cores of active galaxies powered by well-fed black holes, shine like brilliant beacons across billions of light-years. When the quasar's light reaches the Milky Way, it passes through the invisible clouds.

The gas in the clouds absorbs certain frequencies of light, leaving telltale fingerprints in the quasar light. Fox singled out the fingerprint of silicon and used it to trace the gas around the Milky Way. Outflowing and inflowing gas clouds were distinguished by the Doppler shift of the light passing through them—approaching clouds are bluer, and receding clouds are redder.

Currently, the Milky Way is the only galaxy for which we have enough data to provide such a full accounting of gas inflow and outflow.

"Studying our own galaxy in detail provides the basis for understanding galaxies across the universe, and we have realized that our galaxy is more complicated than we imagined," said Philipp Richter of the University of Potsdam in Germany, another co-author on the study.

Future studies will explore the source of the inflowing gas surplus, as well as whether other large galaxies behave similarly. Fox noted that there are now enough COS observations to conduct an audit of the Andromeda galaxy (M31), the closest large galaxy to the Milky Way.

The Hubble Space Telescope is a project of international cooperation between the European Space Agency (ESA) and NASA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Source: HubbleSites/News

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Contact:

Leah Ramsay / Ray Villard

Space Telescope Science Institute, Baltimore, Maryland

667-218-6439 / 410-338-4514

lramsay@stsci.edu/villard@stsci.edu

Andrew Fox

Space Telescope Science Institute, Baltimore, Maryland

afox@stsci.edu

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Related Links:

• The science paper by A. Fox et al.
• NASA's Hubble Portal

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Milky Way’s Center Will Be Revealed by NASA’s Webb Telescope

The center of our Milky Way galaxy is hidden from the prying eyes of optical telescopes by clouds of obscuring dust and gas. But in this stunning vista, the Spitzer Space Telescope's infrared cameras penetrate much of the dust, revealing the stars of the crowded galactic center region. The upcoming Webb telescope will offer a much-improved infrared view, teasing out fainter stars and sharper details. Credits: NASA, JPL-Caltech, Susan Stolovy (SSC/Caltech) et al.

Animation of the Stellar Orbits around the Galactic Center

Infrared observations using the ground-based Keck telescope have allowed astronomers to track individual stars orbiting the black hole at the galactic center. Webb is expected to detect fainter stars than are shown here, providing a more complete census of the stellar population within the galactic core. Credits: Keck/UCLA Galactic Center Group.

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Galactic dust hides swarms of stars and black hole’s glowing disk

To understand galaxies throughout the universe, astronomers start by studying our home galaxy, the Milky Way. Observing the Milky Way is harder than it sounds because vast clouds of dust block light in all directions, particularly toward the galactic center. NASA’s upcoming James Webb Space Telescope will gather infrared light from the center of our galaxy that has passed through the dusty veil. It will examine stellar populations to learn how stars can survive that tumultuous region, which is bathed in harsh ultraviolet and X-ray light and wracked with gravitational tides. And if scientists are lucky, they’ll spot the faint, steady glow from matter spiraling around a supermassive black hole.

The center of our galaxy is a crowded place: A black hole weighing 4 million times as much as our Sun is surrounded by millions of stars whipping around it at breakneck speeds. This extreme environment is bathed in intense ultraviolet light and X-ray radiation. Yet much of this activity is hidden from our view, obscured by vast swaths of interstellar dust.

NASA's upcoming James Webb Space Telescope is designed to view the universe in infrared light, which is invisible to the human eye, but is very important for looking at astronomical objects hidden by dust. After its launch, Webb will gather infrared light that has penetrated the dusty veil, revealing the galactic center in unprecedented detail.

“Even one image from Webb will be the highest quality image ever obtained of the galactic center,” said Roeland van der Marel of the Space Telescope Science Institute (STScI), principal investigator on one planned study that will focus on imaging.

Telescopes on the ground and in space have provided tantalizing glimpses of the residents of the galactic center. Astronomers have tracked stars orbiting the black hole, some of which approach close enough to provide a test of Einstein’s general theory of relativity. However, so far, only the brightest stars are detectable.

“We’re only seeing the tip of the iceberg from the ground. Webb will be able to study fainter stars and tell us more about the overall stellar population,” said Torsten Böker of the European Space Agency and STScI, a co-investigator on a second planned study of the galactic center that will focus on spectroscopy.

Scientists already have been surprised to find low-mass infant stars forming close to the supermassive black hole – some within just a few light-years of its grasp. Theoretically, the black hole's immense gravity and harsh radiation environment should disrupt any gas clouds and prevent them from collapsing into stars. Yet these baby stars called protostars have persisted. Webb's observations may reveal additional protostars, and could provide clues to how stars can form in such an unlikely spot.

Black Hole Mysteries

The Milky Way’s supermassive black hole, known to astronomers as Sagittarius A* (pronounced A-star) also will fall under Webb’s gaze. It is surrounded by a disk of gas and dust, some of which will inevitably fall into the black hole. Astronomers have observed flares of light when the black hole gulped a clump of material. However, they have never detected the steady glow from the black hole's disk.

“Detecting the disk around Sagittarius A* with Webb would be a home run,” Böker said.

Data from Webb also could help address broader questions of how galaxies form — such as the longstanding "chicken and egg" problem of which came first, the galaxy or the black hole.

“Does the black hole come first and stars form around it? Do stars gather together and collide to form the black hole? These are questions we want to answer,” said Jay Anderson of STScI, a co-investigator on one of the studies.

Additionally, studies have shown that the mass of a galaxy’s central black hole is related to the total mass of the surrounding stars, but the reasons for this relationship remain unknown.

“Are there any clues to this mass correlation close to the black hole? Or has recent star formation wiped out signs of what might have happened in the past?” added Marcia Rieke of the University of Arizona, principal investigator on Webb’s NIRCam instrument.

Serendipitous Possibilities

Ultimately, the most exciting results from Webb’s observations might be the unexpected. For example, Webb might find stars in unusual orbits. Or, Webb might spot a gas cloud destined to be ripped apart by gravitational forces.

“We would like to see something unusual, like a star being gobbled up,” said van der Marel.

Ideally, these initial studies of the galactic center will inform future Webb observations. By revisiting the galactic center over a period of several years, astronomers can gain a new understanding of this chaotic region of space.

“So many interesting, strange things happen at the centers of galaxies. We want to find out what’s happening in our own,” said Rieke.

The observations described here will be taken as part of Webb’s Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency

Source: NASA's James Webb Space Telescope/News Release

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Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland
410-338-4366
cpulliam@stsci.edu

Related Links: NASA's Webb Portal

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Astronomers show how supergiant stars repeatedly cool and heat up

The star HR 5271A is one of the four hyper-giants investigated. 

(c) A. Lobel/NASA/Spitzer Space Telescope/IRAC

Source: http://www.astronomie.nl/media/medialibrary/2019/10/HR5171_Spitzer_credit_A_Lobel_NASA_Spitzer.jpg

An international team of professional and amateur astronomers, which includes Alex Lobel, astronomer at the Royal Observatory of Belgium, has determined in detail how the temperature of four yellow hypergiants increases from 4000 degrees to 8000 degrees and back again in a few decades. They publish their findings in the professional journal Astronomy & Astrophysics.

The researchers analysed the light of four yellow hypergiants that has been observed on Earth over the past fifty to one hundred years. Yellow hypergiants are huge, luminous stars. They are fifteen to twenty times heavier than the Sun and shine 500,000 times brighter. The atmospheres of these stars can be so huge that, if they replaced our Sun, they would stretch beyond the orbit of Jupiter.

Because the researchers had such a long series of measurements, they could see in detail how the stars get warmer over decades and cool down in a few years.

The cycle begins with a cool star. In a few decades, the average atmospheric temperature increases to about 8000 degrees. At 8000 degrees, however, the atmosphere becomes unstable due to amplified pulsations. At a certain moment the entire atmosphere erupts. As a result, it cools down quickly and a self-accelerating process occurs in which electrons attach themselves to hydrogen ions and a lot of ionisation energy is released. This cools the atmosphere even further. The cooling from 8000 degrees to 4000 degrees takes only two years.

Then the cycle starts again from the beginning, only with a slightly less massive star. Eventually, astronomers think, the hypergiant transforms into a hotter star and ends its life as a supernova.

During the research, astronomers also found out that one of the four studied hypergiants was not as large as previously assumed. The star, HR5171A, turns out to be much closer than expected.

Source: Royal Observatory of Belgium

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Contact:
 
Alex Lobel
E-mail: alex.lobel@oma.be
Phone number : +32(0)23730348
See also: http://alobel.freeshell.org/hr5171.html

Article:

A.M. van Genderen  et al. (2019), Pulsations, eruptions and evolution of four yellow hypergiants. Accepted for public ation in Astronomy & Astrophysics:https://doi.org/10.1051/0004-6361/201834358. Free preprint: http://arxiv.org/abs/1910.02460

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Two Ancient Migration Events in the Andromeda Galaxy

The globular clusters studied (lower right insets), indicated by colored circles, are located in the outer halo of the Andromeda Galaxy, beyond the bright disk of the galaxy (upper left inset). The star clusters separate into two groups — those associated and unassociated with stellar streams — that have very different orbits, a result that points to two discrete migration events in the history of the galaxy. The color of each circle indicates the line-of-sight velocity of the corresponding star cluster.Credit: Australian National University / NSF's National Optical-Infrared Astronomy Research Laboratory. DownloadJPG1.8MB |TIFF3MB

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Gemini Observatory with NSF’s National Optical-Infrared Astronomy Research Laboratory

Astronomers have uncovered two historic events in which the Andromeda Galaxy underwent major changes to its structure. The findings shed light not only on the evolution and formation of the Andromeda Galaxy, but to our own Milky Way Galaxy as well. Two of the facilities in NSF's National Optical-Infrared Astronomy Research Laboratory, Kitt Peak National Observatory and the International Gemini Observatory, played critical roles in the research, now published in the latest issue of the journal Nature.

Large galaxies like the one we live in, the Milky Way, are believed to grow through repeated merging with smaller, dwarf galaxies. Gas and dwarf galaxies in the vast cosmic web follow the gravitational paths laid out by dark matter — traversing filaments, they migrate slowly toward collections of dark matter and assemble into large galaxies. As dwarf galaxies are pulled in by gravity, they are also pulled apart, leaving behind long trailing streams of stars and compact star clusters.

Astronomers have uncovered evidence for two major migration events in the history of our large galactic neighbor, the Andromeda Galaxy (also known as M31). The more recent migration event occurred a few billion years ago and the older event many billions of years before that. The evidence for the two events comes from “galactic archaeology,” the use of the motions and properties of stars and stellar clusters to reconstruct the formation and evolutionary history of galaxies.

In the case of the Andromeda Galaxy, the team of galactic archaeologists, led by Dr. Dougal Mackey (Australian National University) and Professor Geraint Lewis (University of Sydney), measured the velocities of 77 of the Andromeda Galaxy’s compact star clusters, using the 4-meter Mayall telescope at Kitt Peak National Observatory, the 8-meter Gemini North telescope on Maunakea, Hawai‘i, and other facilities. The star clusters are all located in the outer halo of the galaxy. The outer regions of the galaxy are of particular interest because the dynamical signature of migration events persists longer there.

“By tracing the faint remains of dwarf galaxies with star clusters, we’ve been able to recreate the way the Andromeda Galaxy drew them in at different times, from what’s known as the ‘cosmic web’ of matter that threads the Universe,” Lewis said.

The team found that the star clusters divide into two populations, a young group associated with stellar streams, and an older group that has no such association. The two populations both orbit the Andromeda Galaxy, but their orbital axes are nearly perpendicular to each other.

The different orbits are evidence for two distinct accumulation events. The stellar streams associated with the more recent event are still present, but streams from the older event are long gone.

According to Mackey, reconstructing the formation history of the Andromeda Galaxy provides insights into the history of our own galaxy, the Milky Way.

“One of our main motivations in studying astronomy is to understand our place in the Universe. A way of learning about the Milky Way is to study galaxies that are similar to it, and try to understand how these systems formed and evolved.” Studying the Andromeda Galaxy, “can actually be easier than looking at the Milky Way. Because we live inside it, that can make certain types of observations quite difficult,” Mackey said.

Astronomer Knut Olsen of NSF's National Optical-Infrared Astronomy Research Laboratory, who studies the formation of galaxies but was not part of the study said, “This work shows that galaxies as massive as the Large Magellanic Cloud have merged with the Andromeda Galaxy at least twice in its history.” The Large Magellanic Cloud is a companion galaxy to the Milky Way that is easily visible to the naked eye in the Southern hemisphere. Olsen added, “If we could have observed these events taking place billions of years ago, we would have been treated to a real display of cosmic fireworks as new stars formed!”

“This is a great example of NSF-sponsored facilities being used in unison to unravel the mysteries of our neighbor galaxy M31, something that NSF’s National Optical-infrared Astronomy Research Laboratory should make much easier,” noted Ralph Gaume, Division Director for NSF’s Division of Astronomical Sciences.

Source: Gemini Observatory

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More Information

The study, published in Nature, analyzed data from the Pan-Andromeda Archaeological Survey (PAndAS):“Two major accretion epochs in M31 from two distinct populations of globular clusters,” Mackey et al. 2019, Nature.

NSF’s National Optical-Infrared Astronomy Research Laboratory, the US center for ground-based optical-infrared astronomy, operates the Gemini Observatory, Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and the Large Synoptic Survey Telescope (LSST). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai’i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local Communities in Chile, respectively.

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Science Contacts:

Dr. Dougal Mackey
Research School of Astronomy and Astrophysics
Australian National University, College of Science
Email: dougal.mackey@anu.edu.au
Desk: +61 2 6125 0214
Cell: +61 457 871 313

Professor Geraint Lewis
Sydney Institute for Astronomy
School of Physics, University of Sydney
Email: geraint.lewis@sydney.edu.au
Cell: +61 424 254 551

Dr. Joan Najita
NSF’s National Optical-Infrared Astronomy Research Laboratory
950 N. Cherry Ave. Tucson, AZ 85719 USA
Email: najita@noao.edu
Desk: +1 520-318-8416

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Scientists Observe Year-long Plateaus in Decline of Type Ia Supernova Light Curves

Hubble Space Telescope color composite of SN2013dy within its host galaxy.

Credit: HST, Adam Riess, Or Graur

Low Resolution (jpg)

Hubble Space Telescope color composite of SN2018gv within its host galaxy.

Credit: HST, Adam Riess, Or Graur

Low Resolution (jpg)

Cambridge, MA - Scientists at the Center for Astrophysics | Harvard & Smithsonian have announced the discovery that, contrary to previously accepted knowledge, Type Ia supernovae experience light curve decline plateaus, and lengthy ones at that, lasting up to a year.

CfA scientist Or Graur first noticed strange light curve behaviors while studying late-time Type Ia supernovae in 2015, and this year confirmed light curve plateaus in Type Ia supernovae. "Most supernova research is conducted in the weeks or months immediately following an explosion, but we wanted to see how light curves behave at late times, around 500 to 1000 days after explosion," said Graur. "Optical observations of SN2012gc in 2015 revealed a slowdown in the light curve as expected, but as we studied additional supernovae over time, it became apparent that other mechanisms were at play, so we started looking for patterns to explain what was going on."

To better understand the strange behavior, Graur teamed up with Adam Riess of The Johns Hopkins University and the Space Telescope Science Institute, and 2011 winner of the Nobel Prize in Physics, to study nearby supernovae using Riess's already-set HST programs. "Even though these were all nearby supernovae, at these late times they were very faint. We needed Hubble's resolving power to be able to tell them apart from other stars in their respective galaxies," said Graur. "But what made the difference to our observations was that Adam's programs on Hubble also had near-infrared data in the H-band. What started as a fishing expedition revealed a portion of time where the light curve is flat, and that period lasts for up to a year. That was a surprise. I didn't expect to see that."

The idea of supernova light curve plateaus is not new to cosmology. Type IIP supernovae, which are born of the collapse and explosion of hydrogen-rich red super giants, commonly experience light curve plateaus roughly 100 days in length. Until the discovery of the Type Ia supernova light curve plateau, 100 days was considered a long-period plateau. Type Ia supernova light curve plateaus begin at between 150 and 500 days after explosion, and last approximately 350 days, or nearly a year.

"Up until this moment, the only plateaus seen in any type of supernova were in Type IIP, and they were relatively short compared to what we're seeing in our observations. This is only the second time we've ever seen a plateau like this in a supernova," said Graur. "What we’re seeing is in stark contrast to what we’ve always believed about Type Ia supernovae and it's going to impact the way we apply Type Ia light curves to cosmological models in the future."

The results of the study are published in Nature Astronomy. In addition to Graur—who also serves as a Research Associate at the American Museum of Natural History—and Riess, the study involved CfA scientist Arturo Avelino along with scientists Kate Maguire, Trinity College Dublin; Russell Ryan, Space Telescope Science Institute; Matt Nicholl, University of Edinburgh; Luke Shingles, Queens University Belfast; Ivo R. Seitenzahl, University of New South Wales Canberra; and, Robert Fisher, University of Massachusetts Dartmouth.

About Center for Astrophysics | Harvard & Smithsonian

Headquartered in Cambridge, Mass., the Center for Astrophysics | Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

Amy Oliver, Public Affairs
Fred Lawrence Whipple Observatory
Center for Astrophysics | Harvard & Smithsonian
+1 520-879-4406
amy.oliver@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

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