6 upvotes, 1 direct replies (showing 1)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
There are a couple of things to address here.
So black holes are formed from collapsing stars, right?
Small ones, yeah. We're still figuring out the big ones.
If so, then according to mass conservation, a star's mass equals a black hole's mass, right?
Not exactly, some of it usually gets blown out in the process that creates it, and some mass is carried away by energy in that process as well (including gravitational waves, which for mergers can be enough energy to amount to a substantial fraction of the original mass of the system). But yea, they still obey conservation laws, it's just that not all of the mass will be *in the black hole once you're done*. So if you read an article saying a 20 solar mass star left a 2 solar mass black hole, that's probably why.
So then, if a black hole has enough mass to prevent any lightwaves from escaping, why don't stars?
Gravity depends on two things -- the amount of mass involved, and the distance between the mass. Solar mass black holes aren't black holes because of their large mass, they're black holes because of their small radius. If you can somehow figure out how to get it to collapse to a small enough size, the Sun would become a black hole. Or the Earth. Or your pet hamster. It's just that no natural processes cause that to happen to Earths or hamsters, but there are such processes for massive stars.
Comment by [deleted] at 26/04/2023 at 21:13 UTC
1 upvotes, 2 direct replies
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