Supermassive black holes get displaced from galaxy centres
Washington: The supermassive black hole (SMBH) at the center of the most massive local galaxy, M87, is not where it was expected, a team of astronomy researchers have found.
The research by scientists at Rochester Institute of Technology, Florida Institute of Technology and University of Sussex in the United Kingdom, was conducted using the Hubble Space Telescope.
And they concluded that the supermassive black hole in M87 is displaced from the galaxy centre.
The most likely cause for this supermassive black hole to be off center is a previous merger between two older, less massive, black holes.
"We also find, however, that the iconic M87 jet may have pushed the SMBH away from the galaxy center," said Daniel Batcheldor, who led the investigation.
The study of M87 is part of a wider Hubble Space Telescope project directed by Andrew Robinson, professor of physics at RIT.
"What may well be the most interesting thing about this work is the possibility that what we found is a signpost of a black hole merger, which is of interest to people looking for gravitational waves and for people modelling these systems as a demonstration that black holes really do merge. The theoretical prediction is that when two black holes merge, the newly combined black hole receives a ``kick`` due to the emission of gravitational waves, which can displace it from the centre of the galaxy," said Robinson.
David Merritt, professor of physics at RIT, adds: "Once kicked, a supermassive black hole can take millions or billions of years to return to rest, especially at the center of a large, diffuse galaxy like M87. So searching for displacements is an effective way to constrain the merger history of galaxies."
Jets, such as the one in M87, are commonly found in a class of objects called Active Galactic Nuclei.
It is commonly believed that supermassive black holes can become active as a result of the merger between two galaxies, the in fall of material into the center of the galaxy, and the subsequent merger between their black holes.
Therefore, it is very possible that this finding could also be linked to how active galaxies—including quasars, the most luminous objects in the universe—are born and how their jets are formed.
Because many galaxies have similar properties to M87, it is likely that supermassive black holes are commonly offset from their host galaxy centres.
However, the potential offsets would be very subtle and researchers would rely on the Hubble Space Telescope to detect them.
"Unfortunately, the highest spatial resolution camera onboard HST could not be revived during the recent servicing mission. This means we have to rely on the huge archive of HST data to find more of these vagrant supermassive black holes, as we did for M87," added Batcheldor.
Regardless of the displacement mechanism, the implication of this result is a necessary shift in the classic supermassive black hole paradigm; no longer can it be assumed that all supermassive black holes reside at the centres of their host galaxies.
This may result in some interesting impacts on a number of fundamental astronomical areas, and some interesting questions.
The study will be published in The Astrophysical Journal Letters peer-reviewed scientific journal.
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