- 3748 - BLACKHOLE - massive blackhole missing? Astronomers are searching for signs of a supermassive black hole in the galaxy cluster Abell 2261. Nearly all large galaxies contain central black holes, and the galaxy in the middle of Abell 2261 is expected to contain a particularly massive one.
--------------------- 3748 - BLACKHOLE - massive blackhole missing?
- Scientists think this galaxy underwent a merger with another galaxy in the past, which could have caused a newly formed larger black hole to be ejected. Astronomers do not yet know what happened to this giant black hole.
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- Despite searching with NASA's Chandra X-ray Observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole estimated to weigh between 3 billion and 100 billion times the mass of the Sun is anywhere to be found.
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- This missing black hole should be in the enormous galaxy in the center of the galaxy cluster “Abell 2261“, which is located about 2.7 billion light years from Earth. Nearly every large galaxy in the Universe contains a supermassive black hole in their center, with a mass that is millions or billions of times that of the Sun.
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- Since the mass of a central black hole usually tracks with the mass of the galaxy itself, astronomers expect the galaxy in the center of Abell 2261 to contain a supermassive black hole that rivals the heft of some of the largest known black holes in the Universe.
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- Using Chandra data obtained in 1999 and 2004 astronomers had already searched the center of Abell 2261's large central galaxy for signs of a supermassive black hole. They looked for material that has been superheated as it fell towards the black hole and produced X-rays, but did not detect such a source.
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- Now, 2022, with new, longer Chandra observations a team is making a deeper search for the black hole in the center of the galaxy. They also considered an alternative explanation, in which the black hole was ejected from the host galaxy's center. This violent event may have resulted from two galaxies merging to form the observed galaxy, accompanied by the central black hole in each galaxy merging to form one enormous black hole.
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- When black holes merge, they produce ripples in spacetime called “gravitational waves“. If the huge amount of gravitational waves generated by such an event were stronger in one direction than another, the theory predicts that the new, even more massive black hole would have been sent careening away from the center of the galaxy in the opposite direction.
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- Astronomers have not found definitive evidence for recoiling Blackholes either and it is not known whether supermassive black holes even get close enough to each other to produce gravitational waves and merge; so far, astronomers have only verified the mergers of much smaller black holes.
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- There are two indirect signs that a merger between two massive black holes might have taken place:
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- First, data from the Hubble and Subaru optical observations reveal a galactic core, the central region where the number of stars in the galaxy in a given patch of the galaxy is at or close to the maximum value, that is much larger than expected for a galaxy of its size.
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- The second sign is that the densest concentration of stars in the galaxy is over 2,000 light years away from the center of the galaxy, which is strikingly distant.
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- During a merger, the supermassive black hole in each galaxy sinks toward the center of the newly coalesced galaxy. If they become bound to each other by gravity and their orbit begins to shrink, the black holes are expected to interact with surrounding stars and eject them from the center of the galaxy. This would explain Abell 2261's large core.
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- The off-center concentration of stars may also have been caused by a violent event such as the merger of two supermassive black holes and subsequent recoil of single, larger black hole that results.
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- Even though there are clues that a black hole merger took place, neither Chandra nor Hubble data showed evidence for the black hole itself. Astronomers studied three clumps near the center of the galaxy, and examined whether the motions of stars in these clumps are high enough to suggest they contain a ten billion solar mass black hole. No clear evidence for a black hole was found in two of the clumps and the stars in the other one were too faint to produce useful conclusions.
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- Astronomers also previously studied observations of Abell 2261 with the NSF's Karl G. Jansky Very Large Array. Radio emission detected near the center of the galaxy showed evidence that supermassive black hole activity had occurred there 50 million years ago, but does not indicate that the center of the galaxy currently contains such a black hole.
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- Chandra was used to look for material that had been superheated and produced X-rays as it fell towards the black hole. While the Chandra data did reveal that the densest hot gas was not in the center of the galaxy, they did not reveal any possible X-ray signatures of a growing supermassive blackhole. No X-ray source was found in the center of the cluster, or in any of the clumps of stars, or at the site of the radio emission.
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- There is no black hole at any of these locations, or that it is pulling material in too slowly to produce a detectable X-ray signal. The mystery of this gigantic black hole's location therefore continues.
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- The James Webb Space Telescope may be able to reveal the presence of a supermassive black hole in the center of the galaxy or one of the clumps of stars. If Webb is unable to find the black hole, then the best explanation is that the black hole has recoiled well out of the center of the galaxy.
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- Another mystery is identifying something huge lurking in the shadows of the entire Universe we can see. Known as the “Great Attractor“, unknown mass is causing the Milky Way and all the surrounding galaxies to rush towards it.
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- We would normally have a better understanding of this situation, except for the fact that the Great Attractor happens to lie in the direction behind the galactic bulge, which makes it difficult for us to observe. A team of astronomers have performed a new infrared survey of the region behind the bulge, and they have found yet another large galaxy cluster. Their work is helping to paint a more complete portrait of the environment of the Great Attractor.
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- All galaxies in the Universe are in motion. At the very largest scales this motion is dominated by what astronomers call the “Hubble flow“, which is just the general expansion of the Universe. This causes most galaxies to recede away from each other. But at anything less than fully cosmological scales, there can be extra motion on top of that. For example, the Milky Way and the Andromeda galaxies are on a collision course, and they will merge together in about 5 billion years.
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- In addition to that merger, our two galaxies, along with all the other galaxies in our local group, are rushing towards the Virgo cluster, which is the nearest cluster of galaxies to us.
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- But it doesn’t stop there. The local group, the “Virgo cluster“, and all the other groups and clusters in the nearby region of space are headed in one direction together. Astronomers call the center point of this movement the “Great Attractor“, because it seems to be the largest source of gravity in our local cosmological environment.
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- It just happens that the Great Attractor sits in the direction of our sky behind the galactic bulge. This region of the sky is called the “Zone of Avoidance“, because it’s very difficult for optical telescopes to pierce the thick clouds of dust and gas in this region to develop a clear map of what’s behind it.
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- Astronomers only hope is to use other wavelengths of light that can penetrate gas and dust more easily. One of those wavelengths is infrared. But infrared surveys in this regime is a very difficult task, and so our maps in this region of the universe are incomplete.
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- The team of astronomers have attempted a new survey of the region with the “Gemini South Telescope“, especially targeting a half dozen galaxies within the Zone of Avoidance. They found that the galaxies in their survey were likely to be associated with each other. It’s the first evidence we have that these galaxies might be a member of a much larger cluster of galaxies.
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- This cluster of galaxies isn’t the Great Attractor itself, but it is certainly associated with it. Further observations will hopefully paint a more thorough picture of this new galaxy cluster and its environments, and determine its relationship to the Great Attractor.
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November 22, 2022 BLACKHOLE - massive blackhole missing? 3748
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