Milky Way could hold hundred of rogue black holes: study

The astronomers believe these "intermediate mass" black holes are invisible except in rare circumstances and have been spawned by mergers of black holes within globular clusters -- swarms of stars held together by their mutual gravity.
These black holes are unlikely to pose a threat to Earth, but may engulf nebulae, stars and planets that stray into their paths, the researchers said.
"These rogue black holes are extremely unlikely to do any damage to us in the lifetime of the universe," assistant professor of physics and astronomy at Vanderbilt University in Nashville, Tennessee, Kelly Holley-Bockelmann told AFP.
"Their danger zone, the Schwarzschild radius, (or gravitational radius) is really tiny, only a few hundred kilometers. There are far more dangerous things in our neighbourhood."
The evidence for "intermediate mass" black holes, as opposed to supermassive or stellar-mass black holes, is still largely theoretical and therefore controversial. Only two tentative observations of objects of this sort have been made to date.