Astrophysics: White dwarfs and neutron stars

Eros

Eros
Great video, pretty much nails every aspect of it. Im coming at this as a someone who has a Degree in Physics with Astronomy (and PhD in Particle Physics) and degenerate stars was part of the course that was extremely interesting since we derived both the Chandrasekhar limit and the Tolman–Oppenheimer–Volkoff limit for Electron degeneracy and Neutron degeneracy respectively.

The only mistakes id say is just in terms of language used. At 1:35 - it isn't electron decay that stops the core collapse, the electrons don't decay. What stops the collapse is the compression of the matter to a point to which it becomes electron degenerate, which exerts a pressure outwards produced by filling all electron quantum states. It is very complicated and involved but it is a purely quantum mechanical effect. The material must be concidered as an ideal Fermi-gas, in which no two fermions can occupy the same quantum state. At the temperatures and pressures we are talking about, the core collapse is halted at the point at which you have filled all states up to the fermi-energy. It is such that there is simply no more quantum states open and so an outward pressure is produced halting further collapse.

Same for 2:21 - it isn't neutron decay, its not the protons that decay. - If you take material that is already electron degenerate and compress further, although you maintain electron degeneracy you start to compress the material so much that the location and momentum of the electrons can exist within the nucleus of the carbon and oxygen in the core, this process causes neutronisation of the core, and then you must concider the neutrons as a fermi-gas and do the same process, filling all quantum states up to the fermi-energy for that configuration at which the core compression stops and you form a neutron star.

The complete internal structure of a white dwarf and neutron star are a little speculative, though as you said, I think the internal of a neutron star could be some mix of quark-gluon plasma from what i know of it

Same for a blackhole, it could basically a quark gluon plasma at the core of one of those things. It doesn't in any way have to be a singularity
 

Orvidius

Orvidius
Eros said:
The only mistakes id say is just in terms of language used. At 1:35 - it isn't electron decay that stops the core collapse, the electrons don't decay. What stops the collapse is the compression of the matter to a point to which it becomes electron degenerate, which exerts a pressure outwards produced by filling all electron quantum states. It is very complicated and involved but it is a purely quantum mechanical effect. The material must be concidered as an ideal Fermi-gas, in which no two fermions can occupy the same quantum state. At the temperatures and pressures we are talking about, the core collapse is halted at the point at which you have filled all states up to the fermi-energy. It is such that there is simply no more quantum states open and so an outward pressure is produced halting further collapse.

Same for 2:21 - it isn't neutron decay, its not the protons that decay. - If you take material that is already electron degenerate and compress further, although you maintain electron degeneracy you start to compress the material so much that the location and momentum of the electrons can exist within the nucleus of the carbon and oxygen in the core, this process causes neutronisation of the core, and then you must concider the neutrons as a fermi-gas and do the same process, filling all quantum states up to the fermi-energy for that configuration at which the core compression stops and you form a neutron star.
Click to expand...

Bah, it won't let me rep you. I wanted to point that out as well. No degree here, though. I just took an Astronomy course last year and have done some reading in-between. Armchair scientist, as they say! :D (though it helps that my dad is a Ph.D Astrophysicist).

With the black hole singularity, I think a lot of people still phrase it that way partially due to the swapping of time and a spatial dimension below the event horizon, since it points all possible futures toward the center. Not an expert on that though.
 

Eros

Eros
I don't think it would be so much as a switch of dimensions but an object that is sort of forbidden by a few laws of physics. So the true internal structure of a black hole will probably remain speculative. My comment about it not having to be a singularity is mostly to address the issues with the model. Iv heard a few people basically say that because a singularity is a physically impossible object, it means that blackholes cannot and do not exist. So to suggest that basically there are theoretical ways in which you may have exotic matter or could imagine a similar principle of having degenerate matter basically hold up the structure.

Example of confusing properties
Conservation of angular momentum.
A singularity - that is a object that has zero dimension, cannot have the property of rotation.

Entropy
Entropy is the measure of disorder in a system, and disorder should always increase in a closed system. The singularity has zero volume, so, it should have infinite order (?i think thats the right way around)

How there are ways in which those issues have been modelled from a thermodynamics standpoint, basically in a manner of speaking, associating properties to the event horizon, despite it being a virtual surface. Also it is clear that a blackhole can have the property of rotation in a known spacial axis, based upon what we know about quazars and accretion disk formation, which if the blackhole didn't rotate or have any associated property, the disk would not form, material would simply fall onto the event horizon...

anyway... lol this is getting a bit involved :) and I rapidly approach the limit of both my comprehension of the theory and my memory of it too lol
 

Orvidius

Orvidius
Black holes are pretty brain-twisting for sure. Actually the role-switching of space and time within the black hole is a thing, theoretically. My astrophysicist dad talked with me a little about it, and was pleasantly surprised when I brought it up as something that was covered in a PBS Spacetime episode. They talk about it using Penrose diagrams:

[video=youtube;mht-1c4wc0Q]https://www.youtube.com/watch?v=mht-1c4wc0Q[/video]
 

Ian9989

Ian9989
Very interesting topic, wish I had studied something interesting like this rather then leccy engineering back in the day.

It's heartening to see that as a species we have developed the knowledge and thinking power to even mentally create concepts such as black holes, neutron stars and white dwarfs never mind actually developing the mathematics and physical laws that are needed to work meaningfully with them.

The next great step for this species should be a backward one to take stock and realise what we can achieve if we manage not to wipe ourselves out in the next couple of decades because of what are in reality minor differences in thoughts and beliefs.
 

Eros

Eros
That video explains it very well and makes sense now what you meant by the switch. Still looks not so much a switch and more a change of point of reference, regardless, makes sense now and is also really cleaver! :D
 

Orvidius

Orvidius
Another episode on the dimensional role switching, before the topic gets old. :)

[video=youtube;KePNhUJ2reI]https://www.youtube.com/watch?v=KePNhUJ2reI[/video]
 

CMDRvenerian

CMDRvenerian
Qohen Leth said:
I'll be adding your video in an upcoming fat collection thread, so I'd love to see this grow into a solid Elite Astrophysics series ;)
Click to expand...
That would be with great pleasure! could you notify me when you do that?

Also If anybody has suggestions fro topics I would really appreciate it.
 
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