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rocketsocks t1_ixonaek wrote

When a star exhausts a given fusion fuel in the core it'll undergo gravitational contraction. If the star is very light this might just be the end of things, eventually it'll just be a dead ball of fusion ash. Depending on the mass of the star this process can trigger subsequent eras of fusion reactions with heavier elements. Stars around the mass of our Sun will eventually fuse helium in their cores, and slightly more massive stars will fuse carbon as well, before ending their lives as a burnt out "white dwarf" husk that has lost the remaining hydrogen in the outer layers. Yet more massive stars will continue to fuse elements all the way to iron. And such stars are always so massive that if they can fuse elements up to iron they will also collapse to become either neutron stars or black holes.

When such massive stars (generally over 8 solar masses) near the end of their lives they begin fusing silicon into nickel (which decays into iron). After this point fusion doesn't release energy so it cannot create further heat which would resist gravitational contraction of the nickel and iron plasma core. At some point over the course of literally just a few days of silicon fusion this super dense core becomes large enough that the pressure at the center becomes higher than even electron degenerate "white dwarf" matter can withstand, so it begins collapsing into a neutron star (or even more exotic materials).

The dynamics of this situation are very complicated and depend on things like the spin of the star, the mass (of course), and the metallicity of the outer envelope. Metallicity (the abundance of elements heavier than hydrogen and helium) in the envelope greatly affects energy transport so it can make a huge difference in the evolution of the collapse. The neutron star forms at an enormous temperature as gravitational potential energy is converted into heat from the core contracting from over ten thousand kilometers across to just about 20 kilometers across or so. Beginning from a temperature of over a trillion degrees the neutron star material rapidly cools down via the Urca process through neutrino emission. Over a timescale of about 10 seconds an amount of energy is released in the form of neutrinos equivalent to the Sun's entire output multiplied by 800 billion years (which to be clear is much more energy than the Sun will ever produce). About 1% of that energy ends up deposited in the outer envelope of the dying star, which can heat it up enough that it blows off of the star in a supernova explosion.

If the star is heavy enough then the collapse into a neutron star continues and a neutron star is created that is too massive to resist further collapse into a form of matter dense enough to form a black hole. This could be because the core is too heavy, or it could be because the process of coupling neutrino energy to the outer envelope of the star is ineffective at blowing it away (either due to low metallicity or other factors). The envelope can then fall back onto the neutron star and crush it into a black hole.

This is still the subject of ongoing research but that's the general outline of how you can get a neutron star vs. a black hole.

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reDD1t1ng_ATM t1_ixov44i wrote

This was an amazing explination my friend i started thinking of an explanation in my head after reading his question then after reading yours i was completly empty due to this fantastic explination. Ive always been so intrigued about the make up of black holes like after all that fusion and final collapse what the actual composition of what a black hole becomes. Its gotta be incredible though thats for sure.

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rocketsocks t1_ixp6hpx wrote

A "black hole" is three different things. There's the physical object that creates the black hole, and as far as we can tell in our universe this is usually an object that collapses beyond the density of a neutron star. Likely the extreme pressure from enough mass compresses the neutron star into something like a ball of quark-gluon plasma, but we don't have a ton of knowledge of materials in these conditions so it could be something else as well. When that collapses small enough to form an event horizon everything changes, you have the before times and the after times. After the event horizon forms the outside universe is cut off from the interior of the black hole. It's not only impractical for matter or light to escape the event horizon, it's impossible because there's no space-time trajectories that exist that make that connection, everything is one way, you can enter the event horizon but you can't leave it. At that point whatever the object had been before becomes merely historical trivia for the outside universe, the only thing that's relevant is the event horizon, a phenomenon of space-time. Within the black hole we don't entirely know exactly what happens, and we can't exactly check either so this is still the subject of a lot of ongoing theoretical physics work. Very likely we won't have a good understanding of what happens inside a black hole until we develop a theory of quantum gravity or something equivalent, and it doesn't look like that's going to happen anytime soon.

There is this idea of the information paradox of a black hole due to the fact that they "evaporate" through Hawking radiation. This happens on far too long a timescale to be relevant to human experience, but it's an interesting theoretical problem. In theory Hawking radiation should be uniform, which means that all the quantum information locked away inside the black hole (things like how many protons and electrons fell into it, which in theory are conserved quantities) could essentially get deleted, in seeming violation of conservation laws. There are some interesting theories about how to resolve this paradox, but they are still being developed and it'll be hard to verify them.

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reDD1t1ng_ATM t1_ixxg5n5 wrote

If your not a physicist you should be, this is great stuff. I have 2 questions, 1 being when the black whole forms does it take on the shape of the sphere or just it just take on some wild shape because for it to become sphere like wouldnt it need the grvity of something else pulling on it as well as its own gravity? Number two you mentioned it collapses into quarkplasma like stuf isnt that where the quarks become super quarks where that particle now becomes infections where anything the super quark touches it will also tske on the shape and for of a super quar become very dense and infections as well?

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rocketsocks t1_iy0r3c1 wrote

In Earthly experience quarks are confined within small particles such as protons, neutrons, and other more exotic but short lived particles. Under more extreme conditions quarks can instead exist in a more unconfined form in larger "chunks" than just protons or neutrons. One example being a quark-gluon plasma which requires very high temperatures but is potentially denser than nuclear matter because it can be more highly compressed. Theoretically there might be other states of "quark matter" which might be stable in conditions other than those required to sustain a quark-gluon plasma. This could include "strange matter" and other exotic collections of large numbers of quarks. We've studied quark-gluon plasmas experimentally but we have never created other forms of quark matter so they still remain the subject of speculation and research.

It may be possible that there are routes to creating a higher density object than a neutron star that don't involve a quark-gluon plasma but we don't know for sure. In any event, when a neutron star is crushed down enough (whether via creation of a quark-gluon plasma or through some other form of matter) an event horizon can form. Very early on you'll have a bunch of very high density matter which is still being pushed inward with incredibly force/speed due to collapse and this will feed directly into the event horizon causing it to grow. At some point the rotation of the star/black hole creates a little bit of a delay in how fast matter can fall into the event horizon as an accretion disk forms and that matter takes several seconds to fall in. The black hole feeding on ultra-dense matter in its near proximity releases a lot of energy through the glowing of the accretion disk and the formation of axial jets (due to tightly wound magnetic fields from the accretion disk), creating some of the most energetic events in the universe: gamma ray bursts.

In any event, like everything else in the universe black holes typically have some amount of rotation, which causes the event horizon to have an ellipsoid shape. When an event horizon is created it's sort of like a space-time relic of the gravitational fields of its progenitor. As matter falls into the black hole it basically encapsulates the old event horizon in a new larger event horizon.

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Mikinl t1_ixpgjt3 wrote

Wow thanks for the explanation.

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Siltala t1_ixo5xtu wrote

A star can fuse many things after helium but nothing after iron.

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Ill_Sky4073 t1_ixo8h3d wrote

Mass. If it's massive enough, the star collapses into a black hole because the force of its gravity overcomes the forces that would otherwise prevent it from doing so.

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O5-20 t1_ixof8gn wrote

It depends on the mass of the Star. Only the most massive stars become black holes.

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blpilot t1_ixo5llu wrote

Chandrasekhar limit- about 1.4 solar masses. Above that is what is needed to be a black hole.

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rezallol t1_ixozp5m wrote

if there’s more fuel than the gravity at the end of its life, neutron star, more gravity, blackhole.

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space-ModTeam t1_ixq0fet wrote

Hello u/Brilliant-Fee-690, your submission "Black hole or A neutron star?" has been removed from r/space because:

  • Such questions should be asked in the "All space questions" thread stickied at the top of the sub.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.

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