On the Hunt for a Missing Giant Black Hole

• Astronomers are looking for signs of a supermassive black hole in the galaxy group Abell 2261.
• Almost all major galaxies contain central black holes, and the galaxy in the center of Abell 2261 is expected to contain a particularly massive.
• Scientists believe that this galaxy has undergone a merger with another galaxy in the past, which could have caused a newly formed larger black hole to erupt.
• Despite careful searches with Chandra and other telescopes, astronomers still do not know what happened to this huge black hole.

The mystery surrounding the location of a supermassive black hole deepened.

Despite searching with NASA‘s Chandra X – ray observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole weighs anywhere between 3 billion and 100 billion times the mass of the sun.

This missing black hole must be in the enormous galaxy in the center of the galaxy group Abell 2261, which is located 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 group and in the background, and Chandra X-ray data showing hot gas (pink colored) occurring through the group. The center of the image shows the large elliptical galaxy in the center of the group.

Almost every major galaxy in the universe contains a supermassive black hole in their center, with a mass that is millions or billions of times the mass of the Sun. Since the mass of a central black hole usually traces with the mass of the galaxy itself, astronomers expect that the galaxy in the middle of Abell 2261 will contain a supermassive black hole that is the lever of some of the largest known black holes in the galaxy. universe oppose.

Using Chandra data obtained in 1999 and 2004, astronomers have already searched the center of Abell 2261’s large central galaxy for signs of a supermassive black hole. They searched for material that was overheated when it fell into the black hole and produced X-rays, but did not locate such a source.

With new, longer Chandra observations obtained in 2018, a team led by Kayhan Gultekin of the University of Michigan in Ann Arbor looked deeper into the black hole in the center of the galaxy. They also considered an alternative statement in which the black hole was thrown out of the center of the host system. This violent event may be due to the fact that two galaxies merge into the observed galaxy, accompanied by the central black hole in each galaxy merging into one enormous black hole.

When black holes fuse together, they produce ripples in the said space-time. gravity waves. If the large amount of gravitational waves generated by such an event were stronger in one direction than the other, the theory predicts that the new, even more massive black hole would be removed in the opposite direction from the center of the galaxy. This is called a receding black hole.

Astronomers have not found definitive evidence for the regression of black holes and it is not known whether supermassive black holes even come close enough to each other to produce gravitational waves and merge; so far astronomers have only confirmed the fusion of much smaller black holes. The detection of retrograde supermassive black holes would encourage scientists to use and evolve observatories to search for gravitational waves by fusing supermassive black holes.

The galaxy in the middle of Abell 2261 is an excellent group to look for a receding black hole, as there are two indirect signs that a fusion could have taken place between two massive black holes. 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 spot of the galaxy is at or near the maximum value – which is much larger than what expected for a galaxy of its size. The second sign is that the densest concentration of stars in the galaxy is more than 2,000 light-years away from the center of the galaxy, which is remarkably far away.

These features were first identified by Marc Postman of the Space Telescope Science Institute (STScI) and collaborators in their earlier Hubble and Subaru images, and led them to propose the idea of ​​a merged black hole in Abell 2261. The supermassive black hole during a merger. in each galaxy it sinks to the center of the newly merged galaxy. If they are 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 the great core of Abell 2261. The outer concentration of stars can also be caused by a violent event, such as the fusion of two supermassive black holes and the subsequent recoil of single, larger black holes that results.

Although there are clues that a merger of black holes took place, no data from Chandra or Hubble showed evidence for the black hole itself. Gultekin and most of his co-authors, led by Sarah Burke-Spolaor of the University of West Virginia, used Hubble earlier to search for a bunch of stars that could be carried away by a receding black hole. They studied three clusters near the center of the galaxy and examined whether the motions of stars in these clusters were high enough to indicate that they contained a black hole of ten billion solar masses. No clear evidence of a black hole was found in two of the clusters, and the stars in the other one were too faint to draw useful conclusions.

They also previously studied observations of Abell 2261 with Karl G. Jansky Very Large Array of the NSF. Radio emissions detected near the center of the galaxy have proven that supermassive black hole activity occurred there 50 million years ago, but this does not indicate that the center of the galaxy currently contains such a black hole.

Then they turn to Chandra to look for material that is overheated and produces X-rays while falling to the black hole. While the Chandra data revealed 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 black hole – no X-ray source was in the center of the group not found, or in any of the bunch of stars, or at the place where the radio emission takes place.

The authors concluded that there is no black hole at any of these sites, or that it draws in material too slowly to produce an observable X-ray signal.

The mystery of the location of this huge black hole therefore continues. Although the search was unsuccessful, there is still hope for astronomers who want to search for this supermassive black hole in the future. Once launched, 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 asterisks. If Webb can not find the black hole, the best explanation is that the black hole fell back well out of the center of the galaxy.

A paper describing these results was published in a journal of the American Astronomical Society. Gultekin’s co-authors are Sarah Burke-Spolaor; Tod R. Lauer (National Optical Infrared Astronomy Research Laboratory, Tucson, Arizona); T. Joseph W. Lazio and Leonidas A. Moustakas (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California); and Patrick Ogle and Marc Postman (Space Telescope Science Institute, Baltimore, Maryland).

Reference: “Chandra Observations of Abell 2261 Brightest Cluster Galaxy, a Candidate Host to a Recoiling Black Hole” by Kayhan Gültekin, Sarah Burke-Spolaor, Tod R. Lauer, T. Joseph W. Lazio, Leonidas A. Moustakas, Patrick Ogle and Marc Postman, 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 Astrophysical Observatory controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.