Comment by renox
> The universe could be full of black holes in the asteroid mass range the size of hydrogen atoms.
? Not if there's Hawking radiations.
> The universe could be full of black holes in the asteroid mass range the size of hydrogen atoms.
? Not if there's Hawking radiations.
I'm confused.
Hawking temperature is inversely proportional to the mass. I assume most black holes except the very small ones would thus have a hawking temperature lower than the CMB.
Does that mean that effectively no black holes will ever evaporate not even a tiny bit well until the future time when the CMB will be so red shifted that black holes will start to have net radiation?
Wikipedia suggests that this is the case [0]:
"However, since the universe contains the cosmic microwave background radiation, in order for the black hole to dissipate, the black hole must have a temperature greater than that of the present-day blackbody radiation of the universe of 2.7 K. A study suggests that M must be less than 0.8% of the mass of the Earth – approximately the mass of the Moon."
I'm not sure where the discrepancy between the mass of the Moon vs. an asteroid comes from, though.
[0] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
If the Hawking temperature is below the CMB no net evaporation happens. This means there is a mass cutoff and it’s below asteroid mass. Any smaller PBHs would have evaporated by now assuming we are right about Hawking radiation. The math says it should exist but we have AFAIK not proven it.
The big black holes will last insanely long amounts of time.