Large galaxies may host multiple supermassive black holes

A new study predicts large galaxies like the Milky Way likely host more than one supermassive black hole. This frame from a computer simulation shows how such holes might move about in a host galaxy. Image: Yale

Supermassive black holes, SMBHs, are thought to lurk at the hearts of many, if not all, large galaxies, including Earth’s Milky Way. But when galaxies merge, the smaller galaxy may leave its own SMBH in a wide orbit within the new host.

In a new study, researchers from Yale, the University of Washington, the Institut d’Astrophysique de Paris and University College London predict that galaxies with masses similar to the Milky Way’s should host several supermassive black holes.

The researchers used new cosmological simulation software – Romulus – to predict SMBH dynamics with greater accuracy than previously possible.

Lead author Michael Tremmel, a postdoctoral fellow at the Yale Centre for Astronomy and Astrophysics, said “wandering” SMBHs are predicted to orbit well beyond a host galaxy’s core and disk. As such, they are not likely to pull in more gas, generating detectable radiation, and could be expected to be effectively invisible.

“We are currently working to better quantify how we might be able to infer their presence indirectly,” Tremmel said in a Yale release.

In the meantime, there is no need to worry about an unexpected encounter.

“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 Tremmel. “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.”