What causes pressure in White Dwarfs and Neutron Stars?

In summary: What does this mean?Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist: And to my surprise it is indeed possible to have degenerate matter, resulting from the death of less massive stars!So I'm curious: If these lesser massive stars collapse due to their inability to maintain fusion, how is it that these massive collections of degenerate matter can even exist? How is it possible that you could have (near) pure degenerate matter on such an immense scale?The answer to this is that degeneracy does not cause pressure, it causes an inability to lose heat. Degeneracy does not cause pressure, it causes an inability to
  • #1
Ethan Singer
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Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist: And to my surprise it is indeed possible to have degenerate matter, resulting from the death of less massive stars! So I'm curious: If these lesser massive stars collapse due to their inability to maintain fusion, how is it that these massive collections of degenerate matter can even exist? How is it possible that you could have (near) pure degenerate matter on such an immense scale?

This is an interesting dilemma, because the next obvious question is what causes pressure in these stars? Supposedly the pressure originates from the Pauli-Exclusion principle alone? But considering the size of it's constituent particles, how can these stars have such a large volume?
 
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  • #2
Ethan Singer said:
This is an interesting dilemma, because the next obvious question is what causes pressure in these stars? Supposedly the pressure originates from the Pauli-Exclusion principle alone?

have a read of this and see if it helps ...

https://en.wikipedia.org/wiki/Degenerate_matter

failing that maybe @Ken G can help
 
  • #3
Ethan Singer said:
Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist

What does this mean?

the next obvious question is what causes pressure in these stars?

As in any other type of star: gravity.
 
  • #4
That stars exist at all tells you some important facts about them. Gravity causes them to coalesce and shine and some repulsive force is necessary to prevent them from collapsing. At normal temperature electrostatic repulsion is sufficient to keep particles apart from one another. For a white dwarf electrostatic repulsion is insufficient to resist the gravity drawing particles together. At this point electron degeneracy pressure emerges to maintain the personal space between particles. Should gravity succeed in overwhelming electron degeneracy pressure, as is the case for neutron stars, neutron degeneracy pressure emerges to guard the privacy rights of particles. We do not yet know if there are any additional forces to preserve the sovereignty of particles. Ostensibly, a singularity [aka black hole] results when gravitational force exceeds neutron degeneracy pressure. It is certainly possible forces beyond our current understanding conspire to preclude compression of matter to infinite density. Nature tends to abhor infinites.
 
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The internal structure of stars would not be much different if there were no electrostatic forces, because they are screened out on larger scales, so I don't think electrostatic repulsion has much role in the transition from ideal-gas to degenerate stars. What prevents stars from contracting is gas pressure, and gas pressure depends on the kinetic energy of the particles, not their charge.

The problem with the phrase "degeneracy pressure" is it makes it sound like degeneracy is affecting the pressure somehow, but that's false. What "degeneracy" affects is the way kinetic energy is partitioned among the particles at any given pressure. Importantly, there is a partition that can be reached which renders the gas unable to lose any more heat, and that partition is called "degeneracy," for essentially unknown reasons (it has nothing to do with the concept of degenerate states, in fact it's much more like the opposite of that). The thing to remember is that "degeneracy pressure" actually means "the gas pressure achieved when the gas, due to quantum mechanical effects, can no longer lose heat." The reason this prevents further contraction is that contraction is always caused by heat loss, so when heat cannot be lost, the star cannot contract. So the answer to "what causes pressure" in these stars is: kinetic energy. The answer to "what prevents contraction" in degenerate stars is: an inability to lose heat. Degeneracy does not cause pressure, it causes an inability to lose heat.
 

1. What is the main factor that causes pressure in White Dwarfs and Neutron Stars?

The main factor that causes pressure in White Dwarfs and Neutron Stars is the degeneracy pressure of electrons. This is the result of the Pauli exclusion principle, which states that no two electrons can occupy the same quantum state. As the electron density increases in these dense objects, the electrons are forced into higher energy states, creating a pressure that supports the star against gravitational collapse.

2. How does the temperature of White Dwarfs and Neutron Stars affect the pressure?

The temperature of White Dwarfs and Neutron Stars does not have a significant effect on the pressure. This is because these objects are so dense that their thermal energy is negligible compared to the degeneracy pressure of electrons. However, in some extreme cases, such as in the cores of Neutron Stars, the high temperature can contribute to additional pressure from thermal radiation.

3. Can the pressure in White Dwarfs and Neutron Stars ever be overcome?

It is unlikely that the pressure in White Dwarfs and Neutron Stars can ever be fully overcome. These objects are incredibly dense and have extreme gravitational forces acting on them. The pressure from degenerate electrons is the strongest force holding them together, and it would require a significant amount of energy to overcome it. However, in rare cases, such as in the merger of two Neutron Stars, the pressure can be overcome, resulting in a supernova explosion.

4. Are there any other factors besides degeneracy pressure that contribute to the pressure in White Dwarfs and Neutron Stars?

Yes, in addition to degeneracy pressure, there are other factors that contribute to the pressure in White Dwarfs and Neutron Stars. In Neutron Stars, the strong nuclear force between neutrons also plays a significant role in supporting the star against collapse. Additionally, in White Dwarfs, electron-ion interactions and Coulomb repulsion between nuclei also contribute to the overall pressure.

5. How does the mass of a White Dwarf or Neutron Star affect the pressure?

The mass of a White Dwarf or Neutron Star has a direct impact on the pressure within these objects. As the mass increases, the gravitational forces also increase, causing the star to become more compact and dense. This results in an increase in the degeneracy pressure of electrons, which is the primary force supporting the star against collapse. Therefore, higher-mass White Dwarfs and Neutron Stars have a stronger degeneracy pressure and are more resistant to gravitational collapse.

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