4 ms·

Hawking radiation gives you a lower bound for the size of a primordial black hole that still exists, at 10^15 g. Primordial black holes largely cannot grow, bec

Hawking radiation gives you a lower bound for the size of a primordial black hole that still exists, at 10^15 g. Primordial black holes largely cannot grow, because they would be traveling very fast, likelihood of interaction with ordinary matter is very small, and there is no mechanism that would slow them down. So if there are some in our galaxy, they would just be zipping about at intergalactic speeds until the heat death of the universe, or until they hit the event horizon of a larger black hole and get absorbed. The present-day universe is just too sparse for them to form or accrete material.

weitendorf 2y ago
Not necessarily. That is only the case for black holes with no charge and angular momentum. Given high enough charge and angular momentum for a given mass, black holes become "extremal" and their hawking radiation/temperature approaches zero. It's argued these are unstable or maybe can't even exist for various reasons, but it's a pretty active area of physics AFAICT https://www.quantamagazine.org/mathematicians-prove-hawking-wrong-about-extremal-black-holes-20240821/ https://www.quantamagazine.org/mathematicians-prove-hawking-... That said, if these were primordial I'd expect their charges to not all be 0, so they'd interact with normal matter.