However, one a black hole is kicked out of a galaxy, it will likely “evaporate”.
“...according to the quantum mechanical uncertainty principle, rotating black holes should create and emit particles. Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation.
“Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. Micro black holes (MBHs) are predicted to be larger net emitters of radiation than larger black holes and should shrink and dissipate faster.”
So, there are millions of homeless black holes wandering aimlessly around the universe holding up signs that say, “WILL WORK FOR MASS” ?.............
The rate of Hawking radiation emission (same as ideal black body radiation) is thought to be inversely proportionate to mass according to:
Therefore a million solar mass black hole would be observed at a temperature of about 0.00000000000006 deg K, and would be gaining net mass from both cosmic background radiation at 2.7 K, plus any starshine or other infalling mass source.
In the extremely distant future, if the expanding universe theory is correct, the cosmic background radiation might go low enough to cause a net mass loss...but we're talking trillions of years plus. Even then the rate of evaporation would be very slow.
Bear in mind that the radius of that million solar mass black hole's event horizon is about three million kilometers, so there's not really that much surface area to radiate from - that's only about four times larger than the Sun.