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i got curious why neutron stars don't collapse to black holes: https://www.forbes.com/sites/startswithabang/2018/06/13/the-surprising-reason-why-neutron-stars-

i got curious why neutron stars don't collapse to black holes: https://www.forbes.com/sites/startswithabang/2018/06/13/the-surprising-reason-why-neutron-stars-dont-all-collapse-to-form-black-holes/ https://www.forbes.com/sites/startswithabang/2018/06/13/the-... although it did not explain how black holes form then. do they need a sufficient density of bosons? do those only form in supernovae?

ben_w 6y ago
If you have enough mass (or energy[0]) in a region, it can’t be anything other than a black hole. The relationship between the size of that region and the mass-energy involved is, surprisingly, that the radius (not the volume) is directly proportional to the mass. It gets more complicated for black holes which spin or have a charge, but the basic idea is the same. [0] https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics)
pdonis 6y ago
> it did not explain how black holes form then. do they need a sufficient density of bosons? No. Even degeneracy pressure from the Pauli exclusion principle has a limit; it can't hold an object up against gravity for an arbitrarily large mass. So neutron stars, like white dwarfs, have a maximum mass limit; any object over that mass cannot be a neutron star because neutron degeneracy pressure can't hold it up against its own gravity. (The article briefly mentions this; the limit is the Tolman-Oppenheimer-Volkoff limit.) We don't know exactly what that maximum mass limit is for neutron stars, because we don't know their equation of state with sufficient accuracy (whereas we know the white dwarf equation of state accurately enough to know that the maximum mass limit for them is 1.4 times the mass of the Sun), but we know it's somewhere betweena about 2 and 3 times the mass of the Sun. Objects more massive than that can only be black holes. As far as how black holes form, they form when a sufficiently massive object collapses under its own gravity. Usually this happens when a star runs out of nuclear fuel. (More precisely, this is how black holes of roughly stellar mass form. For supermassive holes, like the one at the center of our galaxy, things are more complicated, because they probably don't form in one single process, they form over a long period of time as a hole that started out a lot smaller swallows other massive objects.) If the collapsing object is over the maximum mass limit for a neutron star, degeneracy pressure from the Pauli exclusion principle cannot stop the collapse.
- danenania 6y ago
  Did all supermassive black holes begin as stellar mass black holes? Is there some other way for them to form?
  - saagarjha 6y ago
    It’s actually not really known how these form. Some theories speculate that they’re normal stellar-mass (with “normal” in this case being hundreds of solar masses, because stars were huge back then) black hope that just ate a lot of stuff. Perhaps they merged with other black holes, too. And it’s also possible that a bunch of dust just collapsed under its own gravity early in the universe’s lifecycle and became dense enough to go directly to a black hole.
  - cipherzero 6y ago
    My understanding is that we're not totally certain if all black holes form from stellar mass black holes. There is a theory that black holes can form from direct collapse. In this case, as I understand it, it can skip the star phase and just collapse straight into a black hole.... but I really am not an expert. You can find more here: https://en.wikipedia.org/wiki/Direct_collapse_black_hole https://en.wikipedia.org/wiki/Direct_collapse_black_hole And I HIGHLY recommend the PBS NOVA episode "Black Hole Apocalypse" (Jan 10, 2018, Season 45 Episode 1). It was on Netflix for a while (and may still be.) Edit: here is the full episode on PBS (thank you NOVA!!!) https://www.pbs.org/video/black-hole-apocalypse-yj34qi/ https://www.pbs.org/video/black-hole-apocalypse-yj34qi/
- milesward 6y ago
  Imagine what an object would look like teetering on that limit, a tiny mote of frozen hydrogen touches down, and now it's over the max, and FOOOOOOOOP the inwards collapse begins...
  - pdonis 6y ago
    For white dwarfs, at least, this process is one possible way to trigger a supernova--a white dwarf right at the limit accretes some more mass and collapses catastrophically; the collapse triggers a supernova explosion.

ben_w 6y ago

If you have enough mass (or energy[0]) in a region, it can’t be anything other than a black hole. The relationship between the size of that region and the mass-energy involved is, surprisingly, that the radius (not the volume) is directly proportional to the mass. It gets more complicated for black holes which spin or have a charge, but the basic idea is the same. [0] https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics)

pdonis 6y ago

> it did not explain how black holes form then. do they need a sufficient density of bosons? No. Even degeneracy pressure from the Pauli exclusion principle has a limit; it can't hold an object up against gravity for an arbitrarily large mass. So neutron stars, like white dwarfs, have a maximum mass limit; any object over that mass cannot be a neutron star because neutron degeneracy pressure can't hold it up against its own gravity. (The article briefly mentions this; the limit is the Tolman-Oppenheimer-Volkoff limit.) We don't know exactly what that maximum mass limit is for neutron stars, because we don't know their equation of state with sufficient accuracy (whereas we know the white dwarf equation of state accurately enough to know that the maximum mass limit for them is 1.4 times the mass of the Sun), but we know it's somewhere betweena about 2 and 3 times the mass of the Sun. Objects more massive than that can only be black holes. As far as how black holes form, they form when a sufficiently massive object collapses under its own gravity. Usually this happens when a star runs out of nuclear fuel. (More precisely, this is how black holes of roughly stellar mass form. For supermassive holes, like the one at the center of our galaxy, things are more complicated, because they probably don't form in one single process, they form over a long period of time as a hole that started out a lot smaller swallows other massive objects.) If the collapsing object is over the maximum mass limit for a neutron star, degeneracy pressure from the Pauli exclusion principle cannot stop the collapse.

danenania 6y ago
Did all supermassive black holes begin as stellar mass black holes? Is there some other way for them to form?
- saagarjha 6y ago
  It’s actually not really known how these form. Some theories speculate that they’re normal stellar-mass (with “normal” in this case being hundreds of solar masses, because stars were huge back then) black hope that just ate a lot of stuff. Perhaps they merged with other black holes, too. And it’s also possible that a bunch of dust just collapsed under its own gravity early in the universe’s lifecycle and became dense enough to go directly to a black hole.
- cipherzero 6y ago
  My understanding is that we're not totally certain if all black holes form from stellar mass black holes. There is a theory that black holes can form from direct collapse. In this case, as I understand it, it can skip the star phase and just collapse straight into a black hole.... but I really am not an expert. You can find more here: https://en.wikipedia.org/wiki/Direct_collapse_black_hole https://en.wikipedia.org/wiki/Direct_collapse_black_hole And I HIGHLY recommend the PBS NOVA episode "Black Hole Apocalypse" (Jan 10, 2018, Season 45 Episode 1). It was on Netflix for a while (and may still be.) Edit: here is the full episode on PBS (thank you NOVA!!!) https://www.pbs.org/video/black-hole-apocalypse-yj34qi/ https://www.pbs.org/video/black-hole-apocalypse-yj34qi/
milesward 6y ago
Imagine what an object would look like teetering on that limit, a tiny mote of frozen hydrogen touches down, and now it's over the max, and FOOOOOOOOP the inwards collapse begins...
- pdonis 6y ago
  For white dwarfs, at least, this process is one possible way to trigger a supernova--a white dwarf right at the limit accretes some more mass and collapses catastrophically; the collapse triggers a supernova explosion.