In a new study, a team of astronomers from Yale Center for Astronomy & Astrophysics, the University of Washington, Institut d’Astrophysique de Paris, and University College London predicts that galaxies with a mass similar to our Milky Way Galaxy should host several supermassive black holes.
Artist’s impression of a massive black hole. Image credit: Alain Riazuelo / CC BY-SA 2.5.
Typically, a supermassive black hole exists at the core of a massive galaxy.
But sometimes they may ‘wander’ throughout their host galaxy, remaining far from the center in regions such as the stellar halo, a nearly spherical area of stars and gas that surrounds the main section of the galaxy.
Astronomers theorize that this phenomenon often occurs as a result of mergers between galaxies in an expanding Universe.
A smaller galaxy will join with a larger, main galaxy, depositing its own, central supermassive black hole onto a wide orbit within the new host.
In the new study, Dr. Michael Tremmel, a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics, and co-authors predict that galaxies with a mass similar to the Milky Way should host several supermassive black holes.
The researchers used a new, state-of-the-art cosmological simulation, Romulus, to predict the dynamics of supermassive black holes within galaxies with better accuracy than previous simulation programs.
“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,” Dr. Tremmel said.
“We estimate that a close approach of one of these wanderers that is able to affect the Solar System should occur every 100 billion years or so, or nearly 10 times the age of the Universe.”
“Since wandering supermassive black holes are predicted to exist far from the centers of galaxies and outside of galactic disks, they are unlikely to accrete more gas — making them effectively invisible,” he added.
“We are currently working to better quantify how we might be able to infer their presence indirectly.”
The results were published this week in the Astrophysical Journal Letters (arXiv.org preprint).
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Michael Tremmel et al. 2018. Wandering Supermassive Black Holes in Milky-Way-mass Halos. ApJL 857, L22; doi: 10.3847/2041-8213/aabc0a
