You’d think that it would be hard to lose one of the largest black holes in the universe. However, scientists are currently being puzzled by the apparent absence of the supermassive black hole at the center of the Abell 2261 galaxy cluster — a monster that is estimated to weigh somewhere between 3 billion and 100 billion times the mass of the sun.
At the center of almost every galaxy, including our own, is a supermassive black hole. These black holes usually scale with the size of the galaxy, so the bigger the galaxy, the bigger the black hole. Abell 2261, which is located 2.7 billion light-years away, has a very large central galaxy and so it should have a similarly large supermassive black hole. But strangely, astronomers have been unable to locate this particular black hole anywhere.
This ongoing puzzle has meant that Abell 2261 has been studied by a variety of instruments over the years, including the Subaru Telescope, the Hubble Space Telescope, and the Chandra X-Ray Observatory. A previous study used data from Chandra to search for the X-rays produced by matter as it falls into the black hole and becomes superheated, but it found no such evidence.
This is very odd indeed, and the latest study probed Chandra’s data even more deeply. It looked for evidence that the black hole had somehow been ejected from its position at the galaxy’s center. While the study didn’t find any evidence of the black hole itself, it did find some suggests that a merger may have taken place.
A merger is a dramatic event when two galaxies merge and the central black holes of each galaxy also merge, throwing out ripples called gravitational waves. If these waves were not evenly distributed in all directions, the black hole could have been set zipping off away from its place at the heart of the galaxy.
This suggestion, called a “recoiling black hole,” is only theoretical as such a thing has never been observed before. But if it is true, it could provide an exciting new way for scientists to study gravitational waves.
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