A supermassive black hole weighing around 3 to 100 billion times the mass of the Sun, is seemingly missing. Astronomers have been searching for this black hole with NASA's Chandra X-ray Observatory and Hubble Space Telescope, but they haven't found evidence of it yet. The black hole is supposed to be located in Abell 2261, an enormous galaxy cluster, which is 2.7 billion light years away from Earth.
Almost every large galaxy has a supermassive black hole at its center which weighs millions or billions of times that of the Sun. Astronomers gathered data from 1999 and 2004, and searched for signs of black hole at the center of Abell. They looked for material that had been super heated as it fell towards the black hole and produced X-rays, but they couldn’t detect any source.
With new observations obtained in 2018, a team at the University of Michigan conducted a deeper search for the galaxy's black hole. They put forward an alternative explanation in which the black hole would have been ejected from the galaxy's center. This could have resulted from two galaxies merging together leading to form the current Abell, and in the event the black holes of both the
galaxies would have merged to form an even bigger one.
When black holes merge, they produce ripples in spacetime called gravitational waves. If a huge amount of gravitational waves generated are stronger in one direction than the other, then the new, big black hole can be sent away from the center of the galaxy in the opposite direction. This is known as 'recoiling black hole'.
Scientists have verified the mergers of small galaxies only so far. It is not yet known whether large galaxies even get close enough to produce gravitational waves and merge.