Black Hole or Newborn Stars? SOFIA Finds Galactic Puzzle

Artist’s concept of a jet from an active black hole that is perpendicular to the host galaxy (left) compared to a jet that is launching directly into the galaxy (right) illustrated over an image of a spiral galaxy from the Hubble Space Telescope. SOFIA found a strange black hole with jets that are irradiating the host galaxy, called HE 1353-1917. The galaxy has 10 times more ionized carbon than its stars could produce. The gas, illustrated in blue in the right image, is concentrated near the galaxy’s center, which indicates that the intense radiation from the black hole’s jet is the source of the excess gas. This contradicts the long-held assumption that ionized carbon primarily indicates the presence of newborn stars, and forces scientists to reevaluate the effect black holes have on galaxies. Credits: ESA/Hubble&NASA and NASA/SOFIA/L. Proudfit

Even celestial objects can seem like they're playing tricks. In a new study, scientists are puzzled by a black hole that seems to be changing its galactic surroundings in a way that is usually associated with newborn stars.

Black holes are inherently strange, with gravitational forces so strong that nothing, not even light, can escape. As active black holes consume gas and dust, some of that material is instead launched outward as jets of high-energy particles and radiation. Usually these jets are perpendicular to the host galaxy, but NASA's Stratospheric Observatory for Infrared Astronomy, or SOFIA, found one that is shooting directly into its galaxy.

That jet is heating up gas around the galaxy's center in a way that's characteristic of stars being born. This is prompting scientists to reevaluate their ideas about a key gas associated with baby stars, and about how black holes affect their host galaxies generally.

“The black hole’s jet orientation is so peculiar,” said Irina Smirnova-Pinchukova, scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany. “It transforms the surroundings in the same way newborn stars would, but stars alone could not cause what we observed.”

Stars are born deep inside celestial clouds of dust and gas, a process hidden from our view in visible light. But infrared light, which our eyes cannot see, can penetrate these clouds. SOFIA, for example, uses infrared light to study how stars are born. But even with powerful telescopes, astronomers cannot see details like newborn stars in extremely distant galaxies. Instead, they hunt for signatures of gas that is heated by newborn stars, called ionized carbon. Because ionized carbon is so often found in connection with newborn stars, scientists often assume star formation is occurring when they find the gas in distant galaxies.

But when scientists on SOFIA studied five nearby galaxies with active black holes, they discovered that the one with the lowest rate of star birth contained the most ionized carbon. In fact, there was 10 times more than in other galaxies of similar size and composition. But the star birth rate is so low that it can only produce 25% of the gas they detected. In other words, newborn stars alone could not explain the abundance of ionized carbon. There must be some other explanation for this important chemical signature.

The team used SOFIA’s instrument called the Field Imaging Far-Infrared Line Spectrometer, or FIFI-LS, to closely examine the galaxy, HE 1353-1917. They found that the black hole’s jet is shooting radiation directly into the galaxy, rather than into the space surrounding it. Most of the ionized carbon is concentrated near the galaxy’s active black hole, indicating that the mysterious source of the gas is the intense radiation the black hole’s jet generates.

This contradicts the long-held assumption that ionized carbon is primarily a signature of newborn stars. The results are published in the journal Astronomy and Astrophysics.

“Without numerous observations of nearby galaxies, we might not find such exceptional cases where a black hole is a source of ionized carbon,” said Smirnova-Pinchukova. “This gas is one of the most important tools we have for studying extremely distant galaxies that cannot be seen in great detail.”

Information from nearby galaxies, such as how black holes can create ionized carbon and affect a galaxy’s subsequent evolution, are crucial for understanding the data from other observatories including the Atacama Large Millimeter/submillimeter Array, or ALMA observatory, in Chile. Radio telescopes like ALMA study some of the most distant and faint galaxies, which are often so far away that even powerful telescopes can only detect them as a point of light. That light is full of information, but details about nearby galaxies gathered by SOFIA are required to interpret data from the most distant regions of the universe. Now scientists know that high levels of ionized carbon in a distant galaxy may indicate not only that a lot of stars are being born, but also that a black hole's jet may be responsible for the same kinds of chemical signatures.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

Media Contact

Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Editor: Kassandra Bell

Source: NASA/Black Holes

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Unpredicted Stellar Black Hole Discovered

Figure LB-1: Accretion of gas onto a stellar black hole from its blue companion star, through a truncated accretion disk (artist impression). Credit: YuJjingchuan, Beijing Planetarium, 2019.

Maunakea, Hawaii – Our Milky Way Galaxy is estimated to contain 100 million stellar black holes – cosmic bodies formed by the collapse of massive stars and so dense even light can’t escape.

Until now, scientists had estimated the mass of an individual stellar black hole in our Galaxy at no more than 20 times that of the Sun. But the discovery of a huge black hole by a Chinese-led team of international scientists has toppled that assumption.

The team, headed by Prof. LIU Jifeng of the National Astronomical Observatory of China of the Chinese Academy of Sciences (NAOC), spotted a stellar black hole with a mass 70 times greater than the Sun.

The monster black hole is located 15 thousand light-years from Earth and has been named LB-1 by the researchers. The discovery is reported in today’s issue of Nature.

The discovery came as a big surprise.

“Black holes of such mass should not even exist in our Galaxy, according to most of the current models of stellar evolution,” said Prof. LIU. “We thought that very massive stars with the chemical composition typical of our Galaxy must shed most of their gas in powerful stellar winds, as they approach the end of their life. Therefore, they should not leave behind such a massive remnant. LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation.”

Until just a few years ago, stellar black holes could only be discovered when they gobbled up gas from a companion star. This process creates powerful X-ray emissions, detectable from Earth, that reveal the presence of the collapsed object.

The vast majority of stellar black holes in our Galaxy are not engaged in a cosmic banquet, though, and thus don’t emit revealing X-rays. As a result, only about two dozen Galactic stellar black holes have been well identified and measured.

To counter this limitation, Prof. LIU and collaborators surveyed the sky with China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), looking for stars that orbit an invisible object, pulled by its gravity.

This observational technique was first proposed by the visionary English scientist John Michell in 1783, but it has only become feasible with recent technological improvements in telescopes and detectors.

Still, such a search is like looking for the proverbial needle in a haystack: only one star in a thousand may be circling a black hole.

After the initial discovery, the world’s largest optical telescopes – Spain’s 10.4-m Gran Telescopio Canarias and W. M. Keck Observatory’s 10-m Keck I telescope on Maunakea, Hawaii – were used to determine the system’s physical parameters. The results were nothing short of fantastic: a star eight times heavier than the Sun was seen orbiting a 70-solar-mass black hole, every 79 days.

The discovery of LB-1 fits nicely with another breakthrough in astrophysics. Recently, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational wave detectors have begun to catch ripples in spacetime caused by collisions of black holes in distant galaxies. Intriguingly, the black holes involved in such collisions are also much bigger than what was previously considered typical.

The direct sighting of LB-1 proves that this population of over-massive stellar black holes exists even in our own backyard. “This discovery forces us to re-examine our models of how stellar-mass black holes form,” said LIGO Director Prof. David Reitze from the University of Florida in the U.S.

“This remarkable result along with the LIGO-Virgo detections of binary black hole collisions during the past four years really points towards a renaissance in our understanding of black hole astrophysics,” said Reitze.

This work was made possible by LAMOST (Xinglong, China), the Gran Telescopio Canarias (Canary Islands, Spain), the W. M. Keck Observatory (Hawaii, United States), and the Chandra X-ray Observatory (United States). The research team comprised scientists from China, the United States, Spain, Australia, Italy, Poland and the Netherlands.

By: Chinese Academy of Sciences Headquarters

Source:  W. M. Keck Observatory/Science News

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Media Contact:

XU Ang, annxu@nao.cas.cn

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About  W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. 

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community.  We are most fortunate to have the opportunity to conduct observations from this mountain.

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Positive Feedback Black Hole: Black Hole Nurtures Baby Stars a Million Light Years Away

 Positive Feedback Black Hole

Credit X-ray: NASA/CXC/INAF/R. Gilli et al.; Radio NRAO/VLA; Optical: NASA/STScI

JPEG (296.7 kb) - Large JPEG (1.9 MB) - Tiff (35.9 MB - More Images

A Tour of a Positive Feedback Black Hole - More Animations

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This image contains a black hole that is triggering star formation across the longest distance ever seen, as described in our latest press release. The black hole is located in the center of a galaxy — identified in a labeled image — about 9.9 billion light years from Earth. In this composite image, X-rays from NASA's Chandra X-ray Observatory (red) have been combined with radio emission detected by the NSF's Karl Jansky Very Large Array, or VLA, (blue), and an optical image from NASA's Hubble Space Telescope (yellow).

As hot gas swirls around the black hole, it emits large amounts of X-rays that Chandra detects. The black hole is also the source of radio-wave emission from a jet of high-energy particles — previously detected by scientists with the VLA — that stretches about a million light years. The jet is also identified in the labeled image. The end of the jet is highlighted by diffuse radio emission caused by the particles slowing down after interacting with surrounding matter. A bright source of radio emission (blue and white) on the opposite side of the black hole marks the end of a second jet of particles. This jet is not visible in the radio image.

Researchers also found a diffuse cloud of X-ray emission surrounding the end of the jet on the left. This X-ray emission is most likely from a gigantic bubble of hot gas heated by the interaction of the jet's particles with surrounding matter. As the hot bubble expanded and swept through four neighboring galaxies it could have created a shock wave that compressed cool gas in the galaxies, causing stars to form. The authors estimate that the star formation rates are between about 100% and 400% higher than typical galaxies with similar masses and distance from Earth.

Positive Feedback Black Hole (labeled)

Credit X-ray: NASA/CXC/INAF/R. Gilli et al.; Radio NRAO/VLA; Optical: NASA/STScI

The black hole's galaxy and the four galaxies with boosted star formation have at least three neighboring galaxies. This system of galaxies was identified using observations with the European Southern Observatory's Very Large Telescope (VLT) and the Large Binocular Telescope (LBT). These galaxies will likely become part of a group or cluster of galaxies that has been caught early in its formation process.

Astronomers have seen many cases where a black hole affects its surroundings through "negative feedback". This occurs when the black hole chokes off star formation because it injects sufficient energy into a galaxy's or a galaxy cluster's hot gas to prevent it from cooling down to make stars. In this newly discovered collection of galaxies, astronomers have found a less common example of positive feedback, where the black hole's effects increase star formation.

The researchers used a total of six days of Chandra observing time spread out over five months. A paper describing these results has been published in the most recent issue of the journal "Astronomy and Astrophysics" and is available online. NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science and flight operations from Cambridge and Burlington, Massachusetts.

A Quick Look at a Positive Feedback Black Hole

Source: NASA’s Chandra X-ray Observatory

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Fast Facts for Positive Feedback Black Hole:

Scale: Image is about 2 arcmin (3.4 million light years) across.
Category: Black Holes, Groups & Clusters of Galaxies
Coordinates (J2000): RA 10h 30m 27s | Dec +05° 24´ 55"
Constellation: Sextans
Observation Date: 10 pointings Jan 17, 2017- May 27, 2017
Observation Time: 132 hours 58 min (5 days 12 hours 58 minutes)
Obs. ID: 18185-18187, 19926, 19987, 19994-19995, 20045-20046, 20081
Instrument: ACIS
References: Gilli, R. et al. 2019; A&A in press. arXiv:1909.00814
Color Code: X-Ray: Red; Radio: Blue; Optical: Yellow
Distance Estimate: About 9.9 billion light years (z=1.7)

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Giant Magnetic Ropes in a Galaxy’s Halo

Composite image of the galaxy NGC 4631, the "Whale Galaxy," revealing large magnetic structures.

Credit: Composite image by Jayanne English of the University of Manitoba, with NRAO VLA radio data from Silvia Carolina Mora-Partiarroyo and Marita Krause of the Max-Planck Institute for Radioastronomy. The observations are part of the project Continuum HAlos in Nearby Galaxies -- an EVLA Survey (CHANG-ES). The optical data were from the Mayall 4-meter telescope, collected by Maria Patterson and Rene Walterbos of New Mexico State University. Arpad Miskolczi of the University of Bochum provided the software code for tracing the magnetic field lines. Hi-Res File

This image of the “Whale Galaxy” (NGC 4631), made with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), reveals hair-like filaments of the galaxy’s magnetic field protruding above and below the galaxy’s disk.

The spiral galaxy is seen edge-on, with its disk of stars shown in pink. The filaments, shown in green and blue, extend beyond the disk into the galaxy’s extended halo. Green indicates filaments with their magnetic field pointing roughly toward us and blue with the field pointing away. This phenomenon, with the field alternating in direction, has never before been seen in the halo of a galaxy.

“This is the first time that we have clearly detected what astronomers call large-scale, coherent, magnetic fields far in the halo of a spiral galaxy, with the field lines aligned in the same direction over distances of a thousand light-years. We even see a regular pattern of this organized field changing direction,” said Marita Krause, of the Max-Planck Institute for Radioastronomy in Bonn, Germany.

An international team of astronomers who are part of a project called the Continuum HAlos in Nearby Galaxies — an EVLA Survey (CHANG-ES), led by Judith Irwin of Queen’s University in Ontario, said the image indicates a large-scale, coherent magnetic field that is generated by dynamo action within the galaxy and spirals far outward in the form of giant magnetic ropes perpendicular to the disk.

“We are a little bit like the blind men and the elephant, since each time we look at the galaxy in a different way we reach a different conclusion about its nature! However, we seem to have one of those rare occasions where a classical theory, about magnetic generators called dynamos, predicted the observations of NGC 4631 quite well. Our dynamo model produces spiralling magnetic fields in the halo that are a continuation of the normal spiral arms in the galaxy’s disc,” said Richard Henriksen, of Queen’s University.

The scientists are continuing their work to further refine their understanding of the galaxy’s full magnetic structure.

The image was made by combining data from multiple observations with the VLA’s giant dish antennas arranged in different configurations to show both large structures and finer details within the galaxy. The naturally-emitted radio waves from the galaxy were analyzed to reveal the magnetic fields, including their directions.

The scientists said the techniques used to determine the direction of the magnetic field lines, illustrated by this image, now can be used on this and other galaxies to answer important questions about whether coherent magnetic fields are common in galactic halos and what their shapes are.

Building such a picture, they said, can answer important questions such as how galaxies acquire magnetic fields, and whether all such fields are produced by a dynamo effect. Can these galaxy halo fields illuminate the mysterious origin of the even larger intergalactic magnetic fields that have been observed?

NGC 4631, 25 million light-years from Earth in the constellation Canes Venatici, is about 80,000 light-years across, slightly smaller than our own Milky Way. It was discovered by the famous British astronomer Sir William Herschel in 1787. This image also shows a companion, NGC 4627, a small elliptical galaxy, just above NGC 4631.

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

The results were reported in the journal Astronomy & Astrophysics.

The theoretical models are described in Woodfinden et al. 2019 MNRAS, 487, 1498.

Source: National Radio Astronomy Observatory (NRAO)/News

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Media Contact:

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Science Contact:

Jayanne English
(204) 474-7105
Jayanne.English@umanitoba.ca

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Sculptor Dwarf Galaxy

The Sculptor dwarf galaxy is a companion to the Milky Way galaxy. Astronomers will use Webb to study the motions of stars in Sculptor and Draco, another dwarf companion to the Milky Way. By studying how the stars move, the researchers will be able to determine how the dark matter is distributed in these galaxies. Credits: NASA, ESA, and R. van der Marel (STScI ). Hi-res image

Studies will help scientists understand dark matter and galaxy formation

By studying dwarf galaxy companions to the Milky Way and the nearby Andromeda galaxy, scientists will learn about galaxy formation and the properties of the mysterious substance called dark matter, which is thought to account for approximately 85% of the matter in the universe. In the first study, astronomers will examine the motions of stars in Draco and Sculptor, two dwarf galaxies that are companions to the Milky Way. By measuring how the stars move, the researchers will be able to determine how the dark matter is distributed in these galaxies. In the second study, the team will observe how four dwarf galaxies move around Andromeda. They hope to determine if those galaxies are grouped within a flat plane in space, like the planets around our Sun. This will provide insights into the process whereby large galaxies form by accretion and accumulation of smaller galaxies.

In two separate studies using NASA’s upcoming James Webb Space Telescope, a team of astronomers will observe dwarf galaxy companions to the Milky Way and the nearby Andromeda galaxy. Studying these small companions will help scientists learn about galaxy formation and the properties of dark matter, a mysterious substance thought to account for approximately 85% of the matter in the universe.

In the first study, the team will gain knowledge of dark matter by measuring the motions of stars in two dwarf companions to the Milky Way. In the second study, they will examine the motions of four dwarf galaxies around our nearest large galactic neighbor, the Andromeda galaxy. This will help determine if some of Andromeda’s satellite galaxies orbit inside a flat plane, like the planets around our Sun. If they do, that would have important implications for understanding galaxy formation. The principal investigator for both programs is Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

Observing Stellar Motions in Dwarf Galaxy Companions to the Milky Way

The nearest galaxies to our own Milky Way are its companion dwarf galaxies, which are much smaller than the Milky Way. Van der Marel and his team plan to study the motions of stars in two of these dwarf galaxies, Draco and Sculptor. The orbits of the stars are governed by the gravity arising from the dark matter in each galaxy. By studying how the stars move, the researchers will be able to determine how the dark matter is distributed in these galaxies.

“How structures in the universe formed depends on the properties of the dark matter that comprises most of the mass in the universe,” explained van der Marel. “So we know there’s dark matter, but we don’t know what actually makes up this dark matter. We just know that there is something in the universe that has gravity and it pulls on things, but we don’t really know what it is.”

The team will study the distribution of dark matter in the centers of the dwarf galaxies to determine the temperature properties of this mysterious phenomenon. If dark matter is “cold,” its density will be very high near the centers of the galaxies. If dark matter is “warm,” it will be more homogenous throughout the area approaching the galactic centers.

At the same time Webb’s Near Infrared Camera (NIRCam) is studying the centers of Draco and Sculptor, another instrument, the Near Infrared Imager and Slitless Spectrograph (NIRISS), will be probing the outskirts of the dwarf galaxies. “These simultaneous observations will provide some insight into how stars move differently near the center and the outskirts of the dwarf galaxies,” said co-investigator Tony Sohn of STScI. “They will also allow two independent measures of the same galaxy, to check for any systematic or instrumental effects.”

Because Webb has approximately six times the light collection area of NASA’s Hubble Space Telescope, the team can measure the motions of stars much fainter than what Hubble can see. The more stars included in a study, the more accurately the team can model the dark matter that influences their motions.

Studying the Motion of Dwarf Galaxy Companions to Andromeda

The nearest large neighbor galaxy of our Milky Way, Andromeda has numerous dwarf galaxy companions, just as the Milky Way does. Van der Marel and his team plan to study how four of those dwarf galaxies are moving around Andromeda, to determine if they are grouped within a flat plane in space, or whether they are moving around Andromeda in all directions.

Unlike the first observation program, the team is not trying to measure how stars inside the dwarf galaxies move. In this study, they are trying to determine how the dwarf galaxies as a whole move around Andromeda. This will provide insights into the process whereby large galaxies form by accretion and accumulation of smaller galaxies, and how exactly that works.

In most models, dwarf galaxies that surround larger galaxies are not expected to lie in a plane. Typically, scientists would expect dwarf galaxies to fly around bigger galaxies in random ways. Slowly, these dwarf companions would lose energy and be accreted into the larger galaxy, which would grow larger still.

However, for both for the Milky Way and Andromeda, several studies have suggested that at least some fraction of the dwarf galaxies lie in a plane, and may even be rotating in that plane. One of the ways to determine if that’s true is to measure their three-dimensional motions. If the motions are actually in the plane, that would suggest that the dwarf galaxies will stay in a plane. But if the companion dwarfs appear to be in a plane but their motions are in all directions, that would indicate a chance alignment and not a long-lasting structure.

If the dwarf galaxies do line up in a plane, that can mean one of several things. It could be that a good fraction of the dwarf companions fell into orbit around Andromeda as a single group. If that were the case, the dwarfs would retain “memory” that they all fell in together, and they would exhibit similar dynamical properties right now.

Another possibility is that the dwarf galaxies of Andromeda formed as what are called “tidal dwarf galaxies.” These gravitationally bound collections of gas and stars form during mergers or interactions between large spiral galaxies. They are as massive as dwarf galaxies but are not dominated by dark matter, as scientists believe most of the dwarf galaxies around us are. It’s possible that a merger of two large galaxies with a lot of gas could form some dwarf galaxies that end up in a single planar structure, but that would be unusual, because scientists don’t think that tidal dwarf galaxies are the predominant type of dwarf galaxy in the universe. Dwarf galaxies are typically known to form inside of dark matter clouds called halos.

Either case could mean that galaxy formation may be more complicated than researchers sometimes think. Either would provide additional constraints on scientists who develop theoretical models of galaxy formation.

Webb’s Extreme Accuracy and Precision

In both programs, the team will push Webb to its limits in terms of accuracy and precision. “It’s a very tricky situation, because basically what we want to measure are very tiny motions,” explained co-investigator Andrea Bellini of STScI. “The accuracy we want to achieve is like measuring something that moves a few inches a year on the surface of the Moon, as seen from Earth.”

Both studies are Guaranteed Time Observations (GTO) programs allocated to the team of the Webb Telescope Scientist, Matt Mountain. He is also president of the Association of Universities for Research in Astronomy (AURA), headquartered in Washington, D.C.

The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries in 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 program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Source: NASA's James Webb Space Telescope/News

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Contact:

Ann Jenkins / Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4366
jenkins@stsci.edu / cpulliam@stsci.edu

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Related Links

• NASA's Webb Portal 
• Video: Are All Galaxies the Same?

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Outback telescope captures Milky Way centre, discovers remnants of dead stars

A radio telescope in the Western Australian outback has captured a spectacular new view of the centre of the galaxy in which we live, the Milky Way.

The image from the Murchison Widefield Array (MWA) telescope shows what our galaxy would look like if human eyes could see radio waves.

This image shows a new view of the Milky Way from the Murchison Widefield Array, with the lowest frequencies in red, middle frequencies in green, and the highest frequencies in blue. Huge golden filaments indicate enormous magnetic fields, supernova remnants are visible as little spherical bubbles, and regions of massive star formation show up in blue. The supermassive black hole at the centre of our galaxy is hidden in the bright white region in the centre. Credit: Dr Natasha Hurley-Walker (ICRAR/Curtin) and the GLEAM Team.

Astrophysicist Dr Natasha Hurley-Walker, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), created the images using the Pawsey Supercomputing Centre in Perth.

“This new view captures low-frequency radio emission from our galaxy, looking both in fine detail and at larger structures,” she said.

“Our images are looking directly at the middle of the Milky Way, towards a region astronomers call the Galactic Centre.”

The data for the research comes from the GaLactic and Extragalactic All-sky MWA survey, or ‘GLEAM’ for short.

The survey has a resolution of two arcminutes (about the same as the human eye) and maps the sky using radio waves at frequencies between 72 and 231 MHz (FM radio is near 100 MHz).

“It’s the power of this wide frequency range that makes it possible for us to disentangle different overlapping objects as we look toward the complexity of the Galactic Centre,” Dr Hurley-Walker said.

“Essentially, different objects have different ‘radio colours’, so we can use them to work out what kind of physics is at play.”

Using the images, Dr Hurley-Walker and her colleagues discovered the remnants of 27 massive stars that exploded in supernovae at the end of their lives.

These are the 27 newly-discovered supernova remnants—the remains of stars that ended their lives in huge stellar explosions thousands to hundreds of thousands of years ago. The radio images trace the edges of the explosions as they continue their ongoing expansion into interstellar space. Some are huge, larger than the full moon, and others are small and hard to spot in the complexity of the Milky Way. Credit: Dr Natasha Hurley-Walker (ICRAR/Curtin) and the GLEAM Team.

These stars would have been eight or more times more massive than our Sun before their dramatic destruction thousands of years ago.

Younger and closer supernova remnants, or those in very dense environments, are easy to spot, and 295 are already known.

Unlike other instruments, the MWA can find those which are older, further away, or in very empty environments.

Dr Hurley-Walker said one of the newly-discovered supernova remnants lies in such an empty region of space, far out of the plane of our galaxy, and so despite being quite young, is also very faint.

“It’s the remains of a star that died less than 9,000 years ago, meaning the explosion could have been visible to Indigenous people across Australia at that time,” she said.

This 28 image photomosaic captures the arch of the milky way over the Guilderton Lighthouse in Western Australia, and the Large and Small Magellanic Clouds. The location of a supernova that would have exploded 9,000 years ago and been visible in the night sky is shown in the image. Credit: Paean Ng / Astrordinary Imaging.

An expert in cultural astronomy, Associate Professor Duane Hamacher from the University of Melbourne, said some Aboriginal traditions do describe bright new stars appearing in the sky, but we don’t know of any definitive traditions that describe this particular event.

“However, now that we know when and where this supernova appeared in the sky, we can collaborate with Indigenous elders to see if any of their traditions describe this cosmic event. If any exist, it would be extremely exciting,” he said. This is a 104 frame photomosaic capturing the Milky Way directly overhead taken at the Pinnacles Desert in Western Australia. A popular tourist location by day and incredible stargazing at night. The location of a supernova that would have exploded 9,000 years ago is shown in the image. Credit: Paean Ng / Astrordinary Imaging.

This is a 104 frame photomosaic capturing the Milky Way directly overhead taken at the Pinnacles Desert in Western Australia. A popular tourist location by day and incredible stargazing at night. The location of a supernova that would have exploded 9,000 years ago is shown in the image. Credit: Paean Ng / Astrordinary Imaging.

Dr Hurley-Walker said two of the supernova remnants discovered are quite unusual “orphans”, found in a region of sky where there are no massive stars, which means future searches across other such regions might be more successful than astronomers expected.

Other supernova remnants discovered in the research are very old, she said.

“This is really exciting for us, because it’s hard to find supernova remnants in this phase of life—they allow us to look further back in time in the Milky Way.”

The MWA telescope is a precursor to the world’s largest radio telescope, the Square Kilometre Array, which is due to be built in Australia and South Africa from 2021.

“The MWA is perfect for finding these objects, but it is limited in its sensitivity and resolution,” Dr Hurley-Walker said.

“The low-frequency part of the SKA, which will be built at the same site as the MWA, will be thousands of times more sensitive and have much better resolution, so should find the thousands of supernova remnants that formed in the last 100,000 years, even on the other side of the Milky Way.”

The new images of the Galactic Centre can be viewed via a web browser using the GLEAMoscope app or through an android device using the GLEAM app.

2017 Best Timelapse: 'GLEAM' by Dr John Goldsmith, Dr Natasha Hurley-Walker and the GLEAM Team from ICRAR on Vimeo.

Source: International Centre for Radio Astronomy Research (ICRAR)/News

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Publication:

‘New candidate radio supernova remnants detected in the GLEAM survey over 345° < l < 60°, 180° < l < 240°’, published in Publications of the Astronomical Society of Australia (PASA) on November 20th, 2019. Paper

‘Candidate radio supernova remnants observed by the GLEAM survey over 345° < l < 60°, 180° < l < 240°’, published in Publications of the Astronomical Society of Australia (PASA) on November 20th, 2019. Paper 

‘GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey II: Galactic Plane 345° < l < 67°, 180° < l < 240°’, published in Publications of the Astronomical Society of Australia (PASA) on November 20th, 2019. Paper

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More Information: 

ICRAR

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia. 

The Murchison Widefield Array 

The Murchison Widefield Array (MWA) is a low-frequency radio telescope and is the first of four Square Kilometre Array (SKA) precursors to be completed. A consortium of partner institutions from seven countries (Australia, USA, India, New Zealand, Canada, Japan, and China) financed the development, construction, commissioning, and operations of the facility. The MWA consortium is led by Curtin University.

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Contacts:

Dr Natasha Hurley-Walker — ICRAR / Curtin University
Ph: +61 8 9266 9178
E:Natasha.Hurley-Walker@curtin.edu.au

Pete Wheeler — Media Contact, ICRAR

Ph: +61 423 982 018

E: Pete.Wheeler@icrar.org

Lucien Wilkinson — Media Contact, Curtin University

Ph: +61 401 103 683

E: Lucien.Wilkinson@curtin.edu.au

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Gas content and quenching of local galaxies

Top panel: gas fraction (fgas) and bottom panel: star formation efficiency (SFE) plotted as functions of distance from the MS in four bins of total stellar mass. Each point corresponds to a median value with a bootstrapped error estimate. The grey shaded area covers the range in ∆SFMS with 10% completeness in each bin.

During galactic transition towards quiescence 'it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars' - suggests a new study led by KICC researchers.

Galaxies in the observable Universe divide into two broad categories: blue, star-forming and red, quiescent. When observed across cosmic, time the distribution of galaxies shifts from the star-formation dominated to passive (quiescent) and hence these two states are interpreted as an evolutionary sequence.

Understanding the physical processes responsible for ceasing star formation is one of the long-standing questions in the area of galaxy evolution. Ultimately, galaxies may quench either due to a lack of fuel or a decrease in star formation efficiency (i.e. an increase in thedepletion time). In order to differentiate between the two possibilities one needs to measure the dense neutral gas within galaxies. However, observing the faint gas emission typically requires long exposure times on premier facilities, thus limiting the sample sizes to only a few hundred detections.

In this work led by Joanna Piotrowska, a PhD student at the Kavli, the KICC researchers use an indirect method to obtain gas mass estimates for ~62 000 local galaxies in the Sloan Digital Sky Survey which allows them to investigate the variation of gas fraction and star formation efficiency of objects on their path towards quiescence. They show that as galaxies deviate from the star-forming Main Sequence (a tight relation between the galaxy stellar mass and star formation rate) it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars as shown in the figure at the above of the page.

These results call for a better understanding of the physical processes driving the decrease in star formation efficiency, which has received relatively little attention in the theory of quenching until now.

You can freely access the article at this link  or with a subscription in the MNRAS Letters here.

Source: Kavli Institute for Cosmology (KICC)/News

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Emission Versus Absorption

NGC 3749

Credit: ESA/Hubble & NASA, D. Rosario et al.

For this Picture of the Week, the NASA/ESA Hubble Space Telescope turned its powerful eye towards an emission line galaxy called NGC 3749. 

When astronomers explore the contents and constituent parts of a galaxy somewhere in the Universe, they use various techniques and tools. One of these is to spread out the incoming light from that galaxy into a spectrum and explore its properties. This is done in much the same way as a glass prism spreads white light into its constituent wavelengths to create a rainbow. By hunting for specific signs of emission from various elements within a galaxy’s spectrum of light — so-called emission lines — or, conversely, the signs of  absorption from other elements — so-called absorption lines — astronomers can start to deduce what might be happening within.

If a galaxy’s spectrum shows many absorption lines and few emission lines, this suggests that its star-forming material has been depleted and that its stars are mainly old, while the opposite suggests it might be bursting with star formation and energetic stellar newborns. This technique known as spectroscopy, can tell us about a galaxy’s type and composition, the density and temperature of any emitting gas, the star formation rate, or how massive the galaxy’s central black hole might be. 

While not all galaxies display strong emission lines, NGC 3749 does! It lies over 135 million light-years away, and is moderately luminous. The galaxy has been used a “control” in studies of especially active and luminous galaxies — those with centres known as active galactic nuclei, which emit copious amounts of intense radiation. In comparison to these active cousins, NGC 3749 is classified as inactive, and has no known signs of nuclear activity.

Source: ESA/Hubble/potw

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NASA’s Fermi, Swift Missions Enable a New Era in Gamma-ray Science

On Jan. 14, 2019, the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory in the Canary Islands captured the highest-energy light every recorded from a gamma-ray burst. MAGIC began observing the fading burst just 50 seconds after it was detected thanks to positions provided by NASA's Fermi and Swift spacecraft (top left and right, respectively, in this illustration). The gamma rays packed energy up to 10 times greater than previously seen. Credits: NASA/Fermi and Aurore Simonnet, Sonoma State University.  Download high-resolution images from NASA’s Scientific Visualization Studio

The fading afterglow of GRB 190114C and its home galaxy were imaged by the Hubble Space Telescope on Feb. 11 and March 12, 2019. The difference between these images reveals a faint, short-lived glow (center of the green circle) located about 800 light-years from the galaxy’s core. Blue colors beyond the core signal the presence of hot, young stars, indicating that this is a spiral galaxy somewhat similar to our own. It is located about 4.5 billion light-years away in the constellation Fornax. Credits: NASA, ESA, and V. Acciari et al. 2019. Download high-resolution images from NASA’s Scientific Visualization Studio

A pair of distant explosions discovered by NASA’s Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory have produced the highest-energy light yet seen from these events, called gamma-ray bursts (GRBs). The record-setting detections, made by two different ground-based observatories, provide new insights into the mechanisms driving gamma-ray bursts.

Astronomers first recognized the GRB phenomenon 46 years ago. The blasts appear at random locations in the sky about once a day, on average.

The most common type of GRB occurs when a star much more massive than the Sun runs out of fuel. Its core collapses and forms a black hole, which then blasts jets of particles outward at nearly the speed of light. These jets pierce the star and continue into space. They produce an initial pulse of gamma rays — the most energetic form of light — that typically lasts about a minute.

As the jets race outward, they interact with surrounding gas and emit light across the spectrum, from radio to gamma rays. These so-called afterglows can be detected up to months — and rarely, even years — after the burst at longer wavelengths.

“Much of what we’ve learned about GRBs over the past couple of decades has come from observing their afterglows at lower energies,” said Elizabeth Hays, the Fermi project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Now, thanks to these new ground-based detections, we’re seeing the gamma rays from gamma-ray bursts in a whole new way.”

Two papers published in the journal Nature describe each of the discoveries. A third paper analyzes one of the bursts using a rich set of multiwavelength data from observatories in space and on the ground. A fourth paper, accepted by The Astrophysical Journal, explores the Fermi and Swift data in greater detail. 

On Jan. 14, 2019, just before 4 p.m. EST, both the Fermi and Swift satellites detected a spike of gamma rays from the constellation Fornax. The missions alerted the astronomical community to the location of the burst, dubbed GRB 190114C.

One facility receiving the alerts was the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory, located on La Palma in the Canary Islands, Spain. Both of its 17-meter telescopes automatically turned to the site of the fading burst. They began observing the GRB just 50 seconds after it was discovered and captured the most energetic gamma rays yet seen from these events.

The energy of visible light ranges from about 2 to 3 electron volts. In 2013, Fermi’s Large Area Telescope (LAT) detected light reaching an energy of 95 billion electron volts (GeV), then the highest seen from a burst. This falls just shy of 100 GeV, the threshold for so-called very high-energy (VHE) gamma rays. With GRB 190114C, MAGIC became the first facility to report unambiguous VHE emission, with energies up to a trillion electron volts (1 TeV). That’s 10 times the peak energy Fermi has seen to date.

“Twenty years ago, we designed MAGIC specifically to search for VHE emission from GRBs, so this is a tremendous success for our team,” said co-author Razmik Mirzoyan, a scientist at the Max Planck Institute for Physics in Munich and the spokesperson for the MAGIC collaboration. “The discovery of TeV gamma rays from GRB 190114C shows that these explosions are even more powerful than thought before. More importantly, our detection facilitated an extensive follow-up campaign involving more than two dozen observatories, offering important clues to the physical processes at work in GRBs.”

These included NASA’s NuSTAR mission, the European Space Agency’s XMM-Newton X-ray satellite, the NASA/ESA Hubble Space Telescope, in addition to Fermi and Swift, along with many ground-based observatories. Hubble images acquired in February and March captured the burst’s optical afterglow. They show that the blast originated in a spiral galaxy about 4.5 billion light-years away. This means the light from this GRB began traveling to us when the universe was two-thirds of its current age.

Another paper presents observations of a different burst, which Fermi and Swift both discovered on July 20, 2018. Ten hours after their alerts, the High Energy Stereoscopic System (H.E.S.S.) pointed its large, 28-meter gamma-ray telescope to the location of the burst, called GRB 180720B. A careful analysis carried out during the weeks following the event revealed that H.E.S.S. clearly detected VHE gamma rays with energies up to 440 GeV. Even more remarkable, the glow continued for two hours following the start of the observation. Catching this emission so long after the GRB’s detection is both a surprise and an important new discovery.

Scientists suspect that most of the gamma rays from GRB afterglows originate in magnetic fields at the jet’s leading edge. High-energy electrons spiraling in the fields directly emit gamma rays through a mechanism called synchrotron emission.

Ground-based facilities have detected radiation up to a trillion times the energy of visible light from a cosmic explosion called a gamma-ray burst (GRB). This illustration shows the set-up for the most common type. The core of a massive star (left) has collapsed and formed a black hole. This “engine” drives a jet of particles that moves through the collapsing star and out into space at nearly the speed of light. The prompt emission, which typically lasts a minute or less, may arise from the jet’s interaction with gas near the newborn black hole and from collisions between shells of fast-moving gas within the jet (internal shock waves). The afterglow emission occurs as the leading edge of the jet sweeps up its surroundings (creating an external shock wave) and emits radiation across the spectrum for some time — months to years, in the case of radio and visible light, and many hours at the highest gamma-ray energies yet observed. These far exceed 100 billion electron volts (GeV) for two recent GRBs. Credits: NASA's Goddard Space Flight Center. Download high-resolution images from NASA’s Scientific Visualization Studio

But both the H.E.S.S. and MAGIC teams interpret the VHE emission as a distinct afterglow component, which means some additional process must be at work. The best candidate, they say, is inverse Compton scattering. High-energy electrons in the jet crash into lower-energy gamma rays and boost them to much higher energies.

In the paper detailing the Fermi and Swift observations, the researchers conclude that an additional physical mechanism may indeed be needed to produce the VHE emission. Within the lower energies observed by these missions, however, the flood of synchrotron gamma rays makes uncovering a second process much more difficult.

“With Fermi and Swift, we don’t see direct evidence of a second emission component,” said Goddard’s S. Bradley Cenko, the principal investigator for Swift and a co-author of the Fermi-Swift and multiwavelength papers. “However, if the VHE emission arises from the synchrotron process alone, then fundamental assumptions used in estimating the peak energy produced by this mechanism will need to be revised.”

Future burst observations will be needed to clarify the physical picture. The new VHE data open a new pathway for understanding GRBs, one that will be further extended by MAGIC, H.E.S.S. and a new generation of ground-based gamma-ray telescopes now being planned.

The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Goddard manages the Swift mission in collaboration with Penn State in University Park, the Los Alamos National Laboratory in New Mexico and Northrop Grumman Innovation Systems in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy.

Source: NASA/Fermi Space Telescope

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By Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Editor: Rob Garner

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Sky survey provides clues to how they change over time

A simulation showing a section of the Universe at its broadest scale. A web of cosmic filaments forms a lattice of matter, enclosing vast voids. Credit: Tiamat simulation, Greg Poole.

A blond boy and a girl with dark hair are skating. The girl is chasing her friend and catching up, so she’s skating faster. When she reaches her friend, she grabs his hand in passing. Because the boy is slower, this sends them both into a rotation around a vertical axis. Credit: Charlotte Welker/brgfx /Freepik 

In the densest regions of the Universe – known as galaxy clusters – the spins of galaxies are expected to be pointing in random directions. But along the flow channels into clusters, our most advanced simulations predict the spins to be aligned along the filament, an effect seen for the first time in the SAMI survey. Credit: Joss Bland-Hawthorn

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The direction in which a galaxy spins depends on its mass, researchers have found.

A team of astrophysicists analysed 1418 galaxies and found that small ones are likely to spin on a different axis to large ones. The rotation was measured in relation to each galaxy’s closest “cosmic filament” – the largest structures in the universe.

The research was driven by the ARC Centre of Excellence in All Sky Astrophysics (ASTRO 3D), based in Australia.

Filaments are massive thread-like formations, comprising huge amounts of matter – including galaxies, gas and, modelling implies, dark matter. They can be 500 million light years long but just 20 million light years wide. At their largest scale, the filaments divide the universe into a vast gravitationally linked lattice interspersed with enormous dark matter voids.

“It’s worth noticing that the spine of cosmic filaments is pretty much the highway of galactic migration, with many galaxies encountering and merging along the way,” says lead researcher Charlotte Welker, an ASTRO 3D researcher working initially at the International Centre for Radio Astronomy Research (ICRAR) and now at McMaster University in Canada.

The filaments are why the universe looks a little like a honeycomb, or a cosmic Aero chocolate bar.

Using data gathered by an instrument called the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) at Australia’s Anglo-Australian Telescope (AAT), Dr Welker, second author and ASTRO 3D principal investigator Professor Joss Bland-Hawthorn from the University of Sydney, and colleagues from Australia, the US, France and Korea studied each of the target galaxies and measured its spin in relation to its nearest filament.

They found that smaller ones tended to rotate in direct alignment to the filaments, while larger ones turned at right angles. The alignment changes from the first to the second as galaxies, drawn by gravity towards the spine of a filament, collide and merge with others, thus gaining mass.

It is a phenomenon that Dr Welker likens to roller-skating in the company of a friend.

“The flip can be sudden,” she says. “Merging with another galaxy can be all it takes.

“Imagine you are skating after a friend and catching up. If you grab your friend’s hand while you are still moving faster, you will both start rotating on a vertical axis – a spin perpendicular to your horizontal path.

“However, if a small cat – a much lighter bit of matter – runs after your friend and jumps on her she probably won’t start spinning. It would take a lot of cats leaping on her at once to change her rotation.”

Co-author Scott Croom from the University of Sydney, also an ASTRO 3D principal investigator, says the result offers insight into the deep structure of the Universe.

“Virtually all galaxies rotate, and this rotation is fundamental to how galaxies form,” he says.

“For example, most galaxies are in flat rotating disks, like our Milky Way. Our result is helping us to understand how that galactic rotation builds up across cosmic time.”

He adds that a new instrument, called Hector, set to be installed at the Anglo Australian Telescope next year, will enable a significant expansion of research in the field.

“Hector will be able to carry out surveys five times larger than SAMI,” he says. “With this we will be able to dig into the details of this spin alignment to better understand the physics behind it.”

The Milky Way, by the way, has a spin well aligned with its nearest cosmic filament, but belongs to a class of intermediate size galaxies that, over all, show no clear tendency towards parallel or perpendicular spins.

“It’s like saying that there is no preference for tea or coffee among a group of people,” says Dr Welker. “Individuals may still prefer either tea or coffee, but overall there is no general tendency towards coffee in the group.”

The research has early access availability in the journal Monthly Notices of the Royal Astronomical Society (MNRS), and is also available in full on the preprint site arxiv.

ASTRO3D is the ARC Centre of Excellence for Astrophysics in 3 Dimensions.

Source: International Centre for Radio Astronomy Research (ICRAR)/News

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Further information

Dr Charlotte Welker: 289 639 1918, time zone is GMT-5; please ask to speak to Dr Welker

Professor Scott Croom: 0450 103 695, time zone is GMT+11

Professor Joss Bland-Hawthorn: 0406 973 133, time zone is GMT+11

Professor Lisa Kewley, ASTRO 3D director: 0451 045 968, time zone is GMT+11

Further assistance: Andrew Masterson: 0488 777 179, time zone is GMT+11

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The paper

The SAMI Galaxy Survey: First detection of a transition in spin orientation with respect to cosmic filaments in the stellar kinematics of galaxies.

MNRS version

Arxiv version

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More about ASTRO 3D

ASTRO 3D is a seven-year $40 million Centre of Excellence project funded by the Australian Government through the Australian Research Council. The Centre began in June 2017 and will end in June 2024. It hosts around 200 investigators and professional staff, mostly based at six nodes: the Australian National University, Curtin University, Swinburne University of Technology, University of Melbourne, University of Sydney, and University of Western Australia.

More about SAMI The SAMI Galaxy Survey began in March 2013, with the intention of creating a large survey of 3000 galaxies across a large range of environment. The key science goals of the SAMI Survey are to answer the following questions:

• What is the physical role of environment in galaxy evolution?
• What is the relationship between stellar mass growth and angular momentum development in galaxies?
• How does gas get into and out of galaxies, and how does this drive star formation?

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More about the Anglo-Australian Telescope.

More about Hector

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Phoenix Cluster: A Weakened Black Hole Allows Its Galaxy to Awaken

Phoenix Cluster

Credit: X-ray: NASA/CXC/MIT/M.McDonald et al; Radio: NRAO/VLA; Optical: NASA/STScI

JPEG (709.2 kb) - Large JPEG (3.1 MB) - Tiff (37.1 MB) - More Images

A Tour of the Phoenix Cluster - More Animations

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The Phoenix galaxy cluster contains the first confirmed supermassive black hole that is unable to prevent large numbers of stars from forming in the core of the galaxy cluster where it resides. This result, reported in our latest press release, was made by combining data from NASA's Chandra X-ray Observatory and Hubble Space Telescope, and the NSF's Karl Jansky Very Large Array (VLA). A new composite image shows data from each telescope. X-rays from Chandra depict hot gas in purple and radio emission from the VLA features jets in red. Optical light data from Hubble show galaxies (in yellow), and filaments of cooler gas where stars are forming (in light blue).

Composite - Phoenix Cluster

Credit: X-ray: NASA/CXC/MIT/M.McDonald et al; Radio: NRAO/VLA; Optical: NASA/STScI

Galaxy clusters are the largest structures in the cosmos that are held together by gravity, and they consist of hundreds or even thousands of galaxies embedded in hot gas and invisible dark matter. The galaxies in their centers of clusters contain the largest supermassive black holes known. In the case of the Phoenix Cluster, the black hole in its core has a mass equivalent to 5.8 billion suns.

For decades, astronomers have found such giant black holes pumping out energy into their environment, which keeps the gas that surrounds them too warm to form many stars. Previous work has shown that the largest galaxies in the universe lack cool gas in their centers and have many fewer stars than expected. The Phoenix Cluster is an example that bucks this trend. Instead, astronomers discovered a relatively cool current of gas along which many stars are being born.

The Phoenix Cluster system has several distinct elements that help tell the story of its unusually high star formation. Data from Chandra show that the coolest gas it can detect is located near the center of the cluster. In the absence of significant sources of heat, astronomers expect cooling to occur at the highest rates in a cluster's center, where the densest gas is located.

Optical observations with Hubble provide evidence for further cooling of gas near the center of the Phoenix Cluster. Ten billion solar masses of cooler gas are located along filaments to the north and south of the black hole, which likely originate from outbursts by the supermassive black hole located in the center of the image. The outbursts generated jets seen in radio waves by the VLA, in two opposite directions. As the jets push outward, they inflated cavities, or bubbles, in the hot gas that pervades the cluster. Chandra's sharp X-ray vision detected these cavities.

Phoenix Cluster

Credit: X-ray: NASA/CXC/MIT/M.McDonald et al; Radio: NRAO/VLA; Optical: NASA/STScI

The filaments of cool gas are located around the borders of the cavities, leading the authors to conclude that the black hole's outburst carries the gas away from the black hole. The farther away from the black hole, the faster the gas can cool to form stars. In the central part of the Phoenix cluster, stars are forming at a rate of about 500 solar masses per year. By comparison stars are forming in the Milky Way galaxy at a rate of about one sun's mass per year.

Eventually the black hole's outburst that is responsible for these jets will generate turbulence, sound waves and shock waves (similar to the sonic booms produced by supersonic aircraft). This will in turn provide a source of heat and prevent further cooling, until the outburst ceases and the build-up of cool gas recommences. The whole cycle can then repeat.

A paper describing these results was published in a recent issue of The Astrophysical Journal, and a preprint is available online. NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science and flight operations from Cambridge and Burlington, Massachusetts.

A Quick Look at the Phoenix Cluster

Source: NASA’s Chandra X-ray Observatory

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Fast Facts for Phoenix Cluster:

Scale: Image is about 45 arcsec (990,000 light years) across.
Category: Groups & Clusters of Galaxies, Quasars & Active Galaxies
Coordinates (J2000): RA 23h 44m 42.00s | Dec -42° 42´ 52.6"v Constellation Phoenix
Observation Date: 12 pointings from Sept 20, 2011 to Jan 25, 2018
Observation Time: 153 hours 7 min (6 days 9 hours 7 minutes)
Obs. ID: 13401, 16135, 16545, 19581-19583, 20630-20631, 20634-20636, 20797
Instrument: ACIS
Also Known As: SPT-CLJ2344-4243
References: McDonald, M. et al., 2019, ApJ, 885, 63; arXiv:1904.08942

Color Code: X-ray: Purple; Radio: Red; Optical: Orange (WFC/F850LP), Green (WFC/F755W), Blue (WFC/F475W)

Distance Estimate: About 5.8 billion light years (z=0.597)

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