- Astronomers are looking for signs of supermass Black hole in the galactic cluster Abell 2261.
- Almost all large galaxies contain central black holes, and the galaxy in the middle of Abel 2261 is expected to be particularly massive.
- Scientists believe that this galaxy has merged with another galaxy in the past, which could have led to the ejection of a newly formed larger black hole.
- Despite careful searches with Chandra and other telescopes, astronomers still do not know what happened to this giant black hole.
The mystery surrounding the location of a supermassive black hole has deepened.
Despite the demand with NASAis the Chandra X – ray Observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole weighing between 3 billion and 100 billion times the mass of the Sun can be found everywhere.
This missing black hole must be in the huge galaxy at the center of the galaxy cluster Abell 2261, which is about 2.7 billion light-years from Earth. This composite image of Abell 2261 contains optical data from Hubble and the Subaru telescope showing galaxies in the cluster and in the background, and X-ray data from Chandra showing hot gas (colored in pink) covering the cluster. In the middle of the image you can see the large elliptical galaxy in the center of the cluster.
Almost every large galaxy in the universe contains a supermassive black hole at its center, with a mass that is millions or billions of times larger than that of the Sun. Because the mass of a central black hole is usually tracked by the mass of the galaxy itself, astronomers expect the galaxy at the center of Abel 2261 to contain a supermassive black hole that rivals the gravity of some of the largest known black holes in the universe.
Using data from Chandra obtained in 1999 and 2004, astronomers have already searched the center of the large central galaxy, Abel 2261, for signs of a supermassive black hole. They looked for material that had overheated as it fell into the black hole and produced X-rays, but found no such source.
Now, with new, longer observations of Chandra received in 2018, a team led by Kaihan Gultekin of the University of Michigan at Ann Arbor has conducted a more in-depth search of the black hole at the center of the galaxy. They also considered an alternative explanation in which the black hole was ejected from the center of the host galaxy. This violent event may be the result of a merger of two galaxies to form the observed galaxy, accompanied by a central black hole in each galaxy that merges to form a huge black hole.
When black holes merge, they create waves in a space-time called gravitational waves. If the vast amount of gravitational waves generated by such an event were stronger in one direction than another, the theory predicts that a new, even more massive black hole would be sent away from the center of the galaxy in the opposite direction. This is called a receding black hole.
Astronomers have found no conclusive evidence of black hole receding, and it is not known whether supermassive black holes even come close enough to produce gravitational waves and merge; so far, astronomers have only checked the mergers of much smaller black holes. Discovering the recoil of supermassive black holes would encourage scientists to use and develop observatories to look for gravitational waves from the fusion of supermassive black holes.
The galaxy at the center of the Abell 2261 is an excellent cluster for searching for a receding black hole, as there are two indirect indications that a merger may have occurred between two massive black holes. First, data from Hubble and Subaru’s optical observations reveal a galactic nucleus – the central region where the number of stars in a galaxy in a region of the galaxy is at or near the maximum value – which is much larger than expected for a galaxy with its size. The second sign is that the densest concentration of stars in the galaxy is more than 2,000 light-years from the center of the galaxy, which is strikingly distant.
These characteristics were first identified by Mark Postman of the Space Telescope Research Institute (STScI) and collaborators in their earlier images of Hubble and Subaru and prompted them to suggest the idea of a unified black hole in Abell 2261. During the merger, the supermassive a black hole in each galaxy sinks toward the center of the newly connected galaxy. If they connect with each other by gravity and their orbit begins to shrink, black holes are expected to interact with surrounding stars and eject them from the center of the galaxy. This would explain the large core of Abell 2261. The concentration of stars outside the center may have been caused by a violent event such as the merger of two supermassive black holes and the subsequent recoil of a single, larger black hole, leading to this.
Although there are indications that a black hole merged, neither Chandra’s nor Hubble’s data have shown evidence of a black hole itself. Gultekin and most of his co-authors, led by Sarah Burke-Spolaor of the University of West Virginia, had previously used Hubble to search for a bunch of stars that might have been swept away by a receding black hole. They studied three lumps near the center of the galaxy and examined whether the motions of the stars in those lumps were high enough to suggest that they contained a ten billion solar mass black hole. No clear evidence of a black hole was found in two of the piles, and the stars in the other were too faint to draw useful conclusions.
Previously, they also studied observations of Abell 2261 with a very large array of NSF by Karl G. Jansky. Radio emissions found near the center of the galaxy show evidence that supermassive black hole activity took place there 50 million years ago, but does not show that the center of the galaxy currently contains such a black hole.
They then turned to Chandra to look for material that overheated and produced X-rays when it fell to the black hole. Although the Chandra data does reveal that the densest hot gas is not in the center of the galaxy, they do not reveal any possible X-ray signatures of a growing supermassive black hole – no X-ray source was found in the center of the cluster, or in any of the star clusters. , or at the location of the radio broadcast.
The authors conclude that either there is no black hole in any of these places, or that it inserts material too slowly to produce a detectable X-ray signal.
Therefore, the mystery of the location of this giant black hole continues. Although the search was unsuccessful, hope remains for astronomers looking for this supermassive black hole in the future. Once launched, James Web Space Telescope may be able to detect the presence of a supermassive black hole in the center of the galaxy or one of the star clusters. If the Web is unable to find the black hole, then the best explanation is that the black hole has receded well from the center of the galaxy.
A report describing these results was published in the Journal of the American Astronomical Society. Gultekin’s co-authors are Sarah Burke-Spolar; Todd R. Lauer (National Laboratory for Optical Infrared Astronomy Research, Tucson, Arizona); T. Joseph W. Lazio and Leonidas A. Moustakas (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA); and Patrick Ogle and Mark Postallon (Space Telescope Science Institute, Baltimore, Maryland).
Reference: Chandra’s Observations on the Brightest Cluster Galaxy Abell 2261, Candidate Host for a Retreating Black Hole by Kaihan Gultekin, Sarah Burke-Spolaor, Todd R. Lauer, T. Joseph W. Lazio, Leonidas A. Mustakas, Patrick Ogle and Mark Postallon, January 5, 2021, The Astrophysical Journal.
DOI: 10.3847 / 1538-4357 / abc483
NASA’s Marshall Space Flight Center manages the Chandra program. The Chandra X-ray Center of the Smithsonian’s Astrophysical Observatory oversees science from Cambridge, Massachusetts and flight operations from Burlington, Massachusetts.