Milky Way and galaxies of similar mass may have more than one supermassive black hole

As a result of galaxy mergers, many supermassive black holes could be wandering around massive galaxies.
By Laurel Kornfeld | Jan 09, 2019
The Milky Way and other galaxies of similar mass may be home to more than one supermassive black hole, with some roaming far from their galactic centers, according to a new study published in Astrophysical Journal Letters.

Using a new cosmological computer simulation known as Romulus, an international team of researchers, including scientists from Yale University, the University of Washington in Seattle,the Institut d'Astrophysique de Paris, and University College London conducted a detailed study of the behavior of supermassive black holes within galaxies.

Most galaxies have supermassive black holes at their centers. However, additional supermassive black holes could be roaming within them, likely the result of mergers between large galaxies and smaller ones.

Such mergers would put the smaller galaxy's central supermassive black hole into a wide orbit in the new and larger merged galaxy.

Over time, these supermassive black holes could wander into their galaxies' stellar halos, outer spherical regions of gas and stars circling the galaxies' main areas, and even out of their galactic discs.

"It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system," said Michael Tremmel of Yale's Center for Astronomy and Astrophysics.

"We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe."

Because these wandering supermassive black holes are not likely to accrete additional gas during their travels, they are essentially invisible to observers and very difficult to find.

"We are currently working to better quantify how we might be able to infer their presence indirectly," he added.



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