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What did you always wonder about #BlackHoles? Something that you always wanted to ask an astronomer working on them?
Collecting questions for a reason, maybe even answering them in the comments (or at a later point).
@vicgrinberg Why are there (hypothesised to be) _small_ black holes? (Primordial ones, for instance.) Without the pressure and gravity of several solar masses' worth of stuff, why wouldn't the black hole matter immediately "pop back out" into being normal matter again? There aren't AFAIK arbitrarily-small neutron stars, for exactly that reason, so why do people think black holes can be small?
@TalesFromTheArmchair @vicgrinberg
Black holes form when something provides enough energy to overcome the pressure that stops things collapsing in on themselves. One of the things that can provide enough energy is gravity, if you have enough of it, and that gravity comes from getting an enormous amount of matter together in one place.
Another way of overcoming that pressure is by smacking things together _really_ hard. If you could smack two peas together hard enough that the matter that made those peas ended up inside their own event horizon, you'd have made a tiny black hole.
There are some very high-energy things whizzing about the universe. If they hit the right things in the right way, they could form tiny black holes.
Regarding the not popping back out again: once that stuff is inside its own event horizon, there's no popping out: nothing crosses the boundary the other way.
@TeaKayB @TalesFromTheArmchair eeeeeh - most things out there in the Universe, even the very high energy ones, don't have enough energy to create black holes. You'd need to get pretty close to the Planck energy (assuming spacetime does not have extra dimensions which we so far seen no evidence of) and there are no known processes that can bring stuff there.
@vicgrinberg @TalesFromTheArmchair
Thanks! So lots of mass _is_ the only feasible route for black hole formation?
@TeaKayB @TalesFromTheArmchair in today's universe: yes! Possible totally absolute fringe cases notwithstanding.
@vicgrinberg @TalesFromTheArmchair
Cool. Are the energies required feasible from, say, a future particle accelerator? Or is that asking too much of human technology?
@TeaKayB @TalesFromTheArmchair Excellent question! No, definitely not. Not even in the big natural space-accelerators such as supernovae etc.
@vicgrinberg @TalesFromTheArmchair
Cool, thanks!