5 ms·

I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principl

I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principle, collapsing the neutrons into an overlapping mass of staggering density. Now that I write that out, I'm a little more doubtful.

btilly 6y ago
Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...
- hinkley 6y ago
  I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.
  - btilly 6y ago
    We understand this one surprisingly well. The seminal paper from 1957 is https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.29.547 https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.29.... that figured out all of the reactions involved. Then used their predictions of the process to predict the distribution of observed isotopes of all of the elements. Those predictions were surprisingly accurate and have been refined more. See https://www.sciencealert.com/this-awesome-periodic-table-shows-the-origins-of-every-atom-in-your-body https://www.sciencealert.com/this-awesome-periodic-table-sho... for the outcome of that. Incidentally the photon takes so long to escape because it gets absorbed and reemitted over and over again in a drunken walk. A supernova is fast because most neutrinos just escape, but with enough being stopped to rip the star to shreds.
- robocat 6y ago
  Your comment did inspire me to go looking for the distribution of elements within the iron core: "carbon, neon, oxygen, and silicon burning leave a core composed of iron, cobalt, nickel, and neighboring species, referred to as the iron-peak nuclei". For anyone else interested in a readable article on a slightly more detailed look at supernova than wikipedia, and a discussion on the difficulties of modelling supernova, I liked this article: https://aip.scitation.org/doi/10.1063/1.4870009 https://aip.scitation.org/doi/10.1063/1.4870009
- deleted 6y ago
  [deleted]
- CRConrad 5y ago
  ...0: A nebula. The -e is a plural marker. Hey, you asked for it.
chasd00 6y ago
seems like i was under the _likely_ incorrect impression black holes have mass but no volume (singularity and all..) and so infinite density. But, then again, what happens beyond the event horizon is meaningless anyway.
- throwawayboise 6y ago
  The description I have heard is that a black hole contains no matter at all, it is all energy expressed as infinitely(?) warped space and time.
jfengel 6y ago
Not exactly. A black hole doesn't have to be very dense. The larger it is, the less dense it needs to be to prevent light from escaping. The supermassive black hole at the center of our galaxy may be less dense than water[1]. For black holes closer to a single solar mass, then yes, they will be super dense, and the degeneracy pressure helps keep it from becoming a black hole. You have to add enough mass to overcome the degeneracy pressure for it to develop the event horizon that makes it a black hole. But not all black holes do that. Others can simply keep acquiring mass without that violent sudden event. They just gradually cross the point where no light can escape, but you might not even notice looking at it. The light just keeps gradually shifting redder and redder until the wavelength becomes infinite. [1] https://en.wikipedia.org/wiki/Sagittarius_A https://en.wikipedia.org/wiki/Sagittarius_A*
- hinkley 6y ago
  Last update I heard on black holes was that the space inside of them increases at the speed of light. That's a hell of a lot of space inside of an event horizon. I'm still fond of the theory that our universe is in fact inside of a black hole, and that the big bang is 'just' the moment we went supercritical. One thing I don't understand about naked singularities - if you were inside of one, the lack of an accretion disk would allow you to see out of it, right? Could you detect that you are looking out across an event horizon?
  - Jweb_Guru 6y ago
    AFAIK the moment you cross an event horizon is not supposed to be significantly different from being just outside of one (at first). Light is one-way within an event horizon though so I imagine that should cause a lot of strange phenomena.
  - R0b0t1 6y ago
    The interesting thing about a naked singularity is you don't have to be "inside" it. You can be next to it but there is no even horizon.

btilly 6y ago

Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...

hinkley 6y ago
I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.
- btilly 6y ago
  We understand this one surprisingly well. The seminal paper from 1957 is https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.29.547 https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.29.... that figured out all of the reactions involved. Then used their predictions of the process to predict the distribution of observed isotopes of all of the elements. Those predictions were surprisingly accurate and have been refined more. See https://www.sciencealert.com/this-awesome-periodic-table-shows-the-origins-of-every-atom-in-your-body https://www.sciencealert.com/this-awesome-periodic-table-sho... for the outcome of that. Incidentally the photon takes so long to escape because it gets absorbed and reemitted over and over again in a drunken walk. A supernova is fast because most neutrinos just escape, but with enough being stopped to rip the star to shreds.
robocat 6y ago
Your comment did inspire me to go looking for the distribution of elements within the iron core: "carbon, neon, oxygen, and silicon burning leave a core composed of iron, cobalt, nickel, and neighboring species, referred to as the iron-peak nuclei". For anyone else interested in a readable article on a slightly more detailed look at supernova than wikipedia, and a discussion on the difficulties of modelling supernova, I liked this article: https://aip.scitation.org/doi/10.1063/1.4870009 https://aip.scitation.org/doi/10.1063/1.4870009
deleted 6y ago
[deleted]
CRConrad 5y ago
...0: A nebula. The -e is a plural marker. Hey, you asked for it.

chasd00 6y ago

seems like i was under the _likely_ incorrect impression black holes have mass but no volume (singularity and all..) and so infinite density. But, then again, what happens beyond the event horizon is meaningless anyway.

throwawayboise 6y ago
The description I have heard is that a black hole contains no matter at all, it is all energy expressed as infinitely(?) warped space and time.

jfengel 6y ago

Not exactly. A black hole doesn't have to be very dense. The larger it is, the less dense it needs to be to prevent light from escaping. The supermassive black hole at the center of our galaxy may be less dense than water[1]. For black holes closer to a single solar mass, then yes, they will be super dense, and the degeneracy pressure helps keep it from becoming a black hole. You have to add enough mass to overcome the degeneracy pressure for it to develop the event horizon that makes it a black hole. But not all black holes do that. Others can simply keep acquiring mass without that violent sudden event. They just gradually cross the point where no light can escape, but you might not even notice looking at it. The light just keeps gradually shifting redder and redder until the wavelength becomes infinite. [1] https://en.wikipedia.org/wiki/Sagittarius_A https://en.wikipedia.org/wiki/Sagittarius_A*

hinkley 6y ago
Last update I heard on black holes was that the space inside of them increases at the speed of light. That's a hell of a lot of space inside of an event horizon. I'm still fond of the theory that our universe is in fact inside of a black hole, and that the big bang is 'just' the moment we went supercritical. One thing I don't understand about naked singularities - if you were inside of one, the lack of an accretion disk would allow you to see out of it, right? Could you detect that you are looking out across an event horizon?
- Jweb_Guru 6y ago
  AFAIK the moment you cross an event horizon is not supposed to be significantly different from being just outside of one (at first). Light is one-way within an event horizon though so I imagine that should cause a lot of strange phenomena.
- R0b0t1 6y ago
  The interesting thing about a naked singularity is you don't have to be "inside" it. You can be next to it but there is no even horizon.