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Astronomers Stunned By Giant Phoenix Galaxy Cluster Breaking Cosmic Records For Making Stars
As vast as the Milky Way may seem, our sprawling galaxy is but a speck next to the largest structures in the universe: galaxy clusters — collections of hundreds to thousands of galaxies bound together by gravity. At the heart of most galaxy clusters sit massive old galaxies, within which only a few new stars are born each year.
Now a multi-institution team led by MIT researchers has identified a galaxy cluster seven billion light-years away that dwarfs most known clusters, churning out a dazzling 740 new stars per year in the central galaxy. The galaxy cluster is among the most massive and most luminous in the universe. While scientists have formally catalogued the cluster by the name SPT-CLJ2344-4243, the MIT-led group has a more informal moniker: the Phoenix cluster, named after the constellation in which it resides.
Astronomers have found an extraordinary galaxy cluster — one of the largest objects in the universe — that is breaking several important cosmic records. The discovery of this cluster, known as the Phoenix Cluster, made with the National Science Foundation’s South Pole Telescope, may force astronomers to rethink how these colossal structures, and the galaxies that inhabit them, evolve.
The Phoenix Cluster, shown here as it appears in microwave (orange), optical (red, green, and blue) and ultraviolet (blue) wavelengths, is forming stars at the highest rate ever observed for the middle of a galaxy cluster. The Phoenix Cluster was discovered by a collaboration of astronomers from the University of Chicago’s Kavli Institute for Cosmological Physics and elsewhere.
Credit: South Pole Telescope collaboration
Follow-up observations made in ultraviolet, optical and infrared wavelengths show that stars are forming in this object at the highest rate ever seen in the middle of a galaxy cluster. The object also is the most powerful producer of X-rays of any known cluster, and among the most massive of clusters. The data also suggest that the rate of hot gas cooling in the central regions of the cluster is the largest ever observed.
Officially known as SPT-CLJ2344-4243, this galaxy cluster has been dubbed the “Phoenix Cluster” because it is located in the constellation of the Phoenix, and because of its remarkable properties. Scientists at the University of Chicago’s Kavli Institute for Cosmological Physics and their collaborators initially found the cluster, located about 5.7 billion light years from Earth, using the Sunyaev-Zel’dovich effect, the shadow that the cluster makes in fossil light leftover from the big bang.
Courtesy of NASA/CXC/M. Weiss
“The mythology of the Phoenix — a bird rising from the dead — is a perfect way to describe this revived object,” said Michael McDonald, a Hubble Fellow at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research. McDonald is the lead author of a paper appearing in the Aug. 16 issue of the journal Nature, which presents these findings. “While galaxies at the center of most clusters have been dead for billions of years, the central galaxy in this cluster seems to have come back to life,” McDonald said.
New findings about an extraordinary galaxy cluster discovered by the National Science Foundation’s 10-meter South Pole Telescope, pictured here, and later followed-up by eight other world-class observatories, appear in the Aug. 16 issue of the journal Nature.
Credit: Daniel Luong-Van
Stars Forming At Incredible Rate
However, most galaxy clusters have formed very few stars over the last few billion years. Astronomers think that the supermassive black hole in the central galaxy of clusters pumps energy into the system, preventing cooling of gas from causing a burst of star formation. The famous Perseus Cluster is an example of a black hole bellowing out energy and preventing the gas from cooling to form stars at a high rate.
With its black hole not producing powerful enough jets, the center of the Phoenix Cluster is buzzing with stars that are forming 20 times faster than in the Perseus Cluster. This rate is the highest seen in the center of a galaxy cluster and is comparable to the highest seen anywhere in the universe.
The frenetic pace of star birth and cooling of gas in Phoenix are causing both the galaxy and the black hole to add mass very quickly — an important phase that the researchers predict will be relatively short-lived.
“The galaxy and its black hole are undergoing unsustainable growth,” said co-author Bradford Benson, a Kavli Institute Fellow at UChicago. “This growth spurt can’t last longer than about a hundred million years, otherwise the galaxy and black hole would become much bigger than their counterparts in the nearby universe.”
Remarkably, the Phoenix Cluster and its central galaxy and supermassive black hole are already among the most massive known objects of their type. Because of their tremendous size, galaxy clusters are crucial objects for studying cosmology and galaxy evolution and so finding one with such extreme properties like the Phoenix Cluster is important.
“The beauty of the SZ effect for cosmology is that it is as easy to detect a cluster of galaxies in the distant reaches of the observable universe as it is for one nearby,” said UChicago’s John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics. “The magnitude of the effect depends on the mass of the object and not its distance from Earth.”
Galaxy clusters contain enough hot gas to create detectable “shadows” in the light left over from the big bang, which also is known as the cosmic microwave background radiation. This light has literally travelled for 14 billion years across the entire observable universe to get to Earth. If it passes through a massive cluster on its way, then a tiny fraction of the light gets scattered to higher energies — the Sunyaev-Zel’dovich effect.
The South Pole Telescope collaboration has now completed an SZ survey of a large region of the sky finding hundreds of distant, massive galaxy clusters. Further follow-up observations of the clusters at X-ray and other wavelengths may reveal the existence of additional Phoenix-like galaxy clusters.
Also contributing observations of the Phoenix Cluster were the Gemini Observatory and the Blanco 4-meter and Magellan telescopes, all in Chile, while several space-based telescopes were used to measure the cluster’s star-formation rate.
Until now, evidence for what astronomers suspect happens at the cores of the largest galaxy clusters has been uncomfortably scarce. Theory predicts that cooling flows of gas should sink toward the cluster’s center, sparking extreme star formation there, but so far – nada, zilch, not-so-much.
The situation changed dramatically when a large international team of over 80 astronomers, led by Massachusetts Institute of Technology’s Hubble Fellow Michael McDonald, studied a recently discovered (yet among the largest-known) galaxy cluster. The team found evidence for extreme star formation, or a starburst, significantly more extensive than any seen before in the core of a giant galaxy cluster. “It is indeed reassuring to see this process in action,” says McDonald. “Further study of this system may shed some light on why other clusters aren’t forming stars at these high rates, as they should be.”
The result, published in the August 16th issue of the journal Nature, began developing in 2010 when data from the South Pole Telescope (SPT) allowed astronomers to identify the huge cluster of galaxies some 5.7 billion light-years distant. Designated SPT-CLJ2344-4243, it is among the largest galaxy clusters in the universe.
“Our first observations of this cluster with the Gemini South telescope in Chile really helped to ignite this work,” says McDonald. “They were the first hints that the central galaxy in this cluster was such a beast!” The paper’s second author, Matthew Bayliss of Harvard University, adds, “When I first saw the Gemini spectrum, I thought we must have mixed up the spectra, it just looked so bizarre compared to anything else of its kind.” Bayliss and Harvard graduate student Jonathan Ruel used the Gemini data to determine the cluster’s distance; they also corroborated its huge mass with estimates from X-ray data obtained with the Chandra X-ray Observatory. Additional survey data from the National Optical Astronomy Observatory’s (NOAO) Blanco Telescope in Chile augmented the early characterization of this cluster. A Blanco image of the cluster (Figure 1, top) is available as part of this press release.
Optical/UV/X-ray composite with a pull-out from the central region to optical/UV image.
Image courtesy of the Chandra X-ray Observatory.
With this result, astronomers now believe they have finally seen, at least in this one large cluster of galaxies, what they expected to find all along – a massive burst of star formation, presumably fueled by an extensive flow of cooling gas streaming inward toward the cluster’s central core galaxy. The sinking gas is likely sparking star formation and a lively, dynamic environment – somewhat like a cold front triggering thunderstorms on a hot summer’s day. This is in rich contrast to most other large galaxy clusters where central galaxies appear to have stopped forming new stars billions of years ago – an uncomfortable discrepancy known as the “cooling-flow problem.”
According to theory, the hot plasma that fills the spaces between galaxy cluster members should glow in X-rays as it cools, in much the same way that hot coals glow red. As the galaxy cluster forms, this plasma initially heats up due to the gravitational energy released from the infall of smaller galaxies. As the gas cools, it should condense and sink inward (known as a cooling flow). In the cluster’s center, this cooling flow can lead to very dense cores of gas, termed “cool cores,” which should fuel bursts of star formation in all clusters that go through this process. Most of these predictions had been confirmed with observations—the X-ray glow, the lower temperatures at the cluster centers— but starbursts accompanying this cooling remain rare.
SPT-CLJ2344-4243, nicknamed the “Phoenix Cluster, lies in the direction of the southern constellation Phoenix, which McDonald suggests is fitting. “The mythology of the Phoenix – a bird rising from the dead – is a great way to describe this revived object,” says McDonald. “While galaxies at the center of most clusters may have been dormant for billions of years, the central galaxy in this cluster seems to have come back to life with a new burst of star formation.”
The team combined multiple ground- and space-based observations including data from the Gemini South 8-meter and the NOAO Blanco 4-meter telescopes, both in Chile and funded with support by the U.S. National Science Foundation (as is the South Pole Telescope which made the initial discovery of this galaxy cluster in 2010). Observations critical to this research also included the Chandra X-ray Observatory, NASA’s WISE and GALEX observatories, and the European Space Agency’s Herschel Observatory.
The new galaxy cluster may shed new light on a decades-old astrophysical conundrum termed the “cooling flow problem.” Gas at the core of a cluster, spewed from nearby galaxies and supernova explosions, should naturally cool over time, forming a flow cold enough to condense and form new stars. However, scientists have been unable to identify any galaxy cluster that does, in fact, cool at the rates predicted.
One explanation, McDonald says, may be that a cluster’s natural cooling is somehow interrupted. He cites the Perseus cluster as an example: The black hole at the center of this cluster emits jets of particles that may act to reheat the core, preventing it from cooling completely.
The image on the left shows the newly discovered Phoenix Cluster, located about 5.7 billion light years from Earth. This composite includes an X-ray image from NASA’s Chandra X-ray Observatory in purple, an optical image from the 4m Blanco telescope in red, green and blue, and an ultraviolet (UV) image from NASA’s Galaxy Evolution Explorer (GALEX) in blue. The Chandra data reveal hot gas in the cluster and the optical and UV images show galaxies in the cluster and in nearby parts of the sky.
Credit: Credits: X-ray: NASA/CXC/MIT/M.McDonald; UV: NASA/JPL-Caltech/M.Mc
“What’s interesting about the Phoenix cluster is that we see almost all the cooling that was predicted,” McDonald says. “It could be that this is earlier in the evolution where there’s nothing stopping it, so it cools and becomes a starburst … in fact, there are few things forming stars in the universe faster than this galaxy.”
Getting the complete view
The Phoenix cluster was first detected in 2010 by researchers using the South Pole Telescope, a 10-meter-wide telescope in Antarctica that scans huge patches of the sky for new galaxy clusters. McDonald and his colleagues recently used the space-based Chandra X-Ray Observatory to study the most massive clusters identified by the South Pole Telescope. Immediately, the Phoenix cluster stood out in the X-ray data as the brightest of the clusters — a finding that prompted McDonald to follow up with more observations of the cluster from more telescopes.
Microwave (orange), optical (red, green, blue) and ultraviolet (blue) image of the Phoenix Cluster.
The team ultimately acquired images of the Phoenix cluster from 10 different telescopes in space and on the ground around the world. Each telescope observed the cluster at different wavelengths, illuminating different features of it.
“The central black hole is very bright in the X-ray, but the star formation is very bright in the optical and ultraviolet,” McDonald says. “So you need to work together with all these different telescopes to get a complete view.”
The team combined data from all 10 telescopes to determine the galaxy cluster’s mass and luminosity. To calculate the mass, the group first measured the cluster’s temperature, which was estimated by observing the cluster’s peak wavelength. McDonald explains that the wavelength at which an object peaks reveals information about its temperature — so the researchers identified the Phoenix cluster’s peak wavelength in the X-ray spectrum, then calculated its temperature.
From the cluster’s temperature, the group calculated its mass: The hotter a ball of gas, the greater its overall mass. The researchers found the Phoenix cluster is easily among the most massive clusters in the universe.
The group then looked for signs of star formation; new stars are particularly bright in the ultraviolet, and the researchers found that ultraviolet images taken of the cluster revealed hundreds of young stars in its core. The cluster’s extreme luminosity also indicated that it was cooling very rapidly, most likely providing the fuel for star formation.
Brian McNamara, a professor of astrophysics at the University of Waterloo, says the extreme starburst identified by the group may illustrate how the most massive primeval galaxies may have formed. He adds that the Phoenix cluster’s exceptional behavior may result from a faulty mechanism at its core.
“It shows cooling and star formation during a phase when the supermassive black hole lurking in the galaxy’s nucleus seems to be asleep at the switch,” McNamara says. “But once the black hole gets going and begins to push the hot atmosphere aside, perhaps in another 100 million years or so, it should shut down cooling and reduce the star formation rate in a feedback process that is active in most galaxy clusters.”
McDonald hopes to access the Hubble Space Telescope to continue studying this massive galaxy cluster. “You’d see these fantastic blue filaments where stars are forming out of cooling streams,” McDonald says. “It should look quite remarkable, instead of our ground-based images which show a blob of blue light.”
As for the cluster’s seemingly anomalous cooling, McDonald guesses that perhaps the phenomenon is not as exceptional as it appears.
“It could be a timing thing, where 1 percent of the time you get this vigorous star formation and runaway cooling,” McDonald says. “It might be that every cluster we see goes through this phase, but it’s so short-lived that this is the only one we’ve found. And we were in the right place at the right time.”
Contacts and sources:’
Steve Koppes
University of Chicago
Chandra X-ray Observatory
Peter Michaud
Gemini Observatory, Hilo, HI
Antonieta Garcia
Gemini Observatory, La Serena, Chile
MIT
Over 99.99% of the entire universe (including every star) is composed of ionized plasma, whose ability to conduct electricity is infinite. The cosmos is also wired with electro-magnetic filaments. The most sensible way to comprehend the nature of the heavens is to liken it to a Christmas tree strewn with multi-colored electric light bulbs celebrating the birth of Christ, who is the Second Person of the Holy Trinity (the Creator and Governor of all things, visible and invisible.)
If the Universe is `4.5 billion` years of age, how the hell can something `5.7 billion` years old be detected?
The universe is estimated to be approximately 13.7 billion years old. God created i and governs it, but Obama thinks he is greater than God. Other pathetic megalomaniacs have made the same mistake, only to eventually discover that they were dead wrong.