Learning Physics: How Do Neutron Stars Form?

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Discussion Overview

The discussion centers around the formation of neutron stars, exploring the underlying physical processes and pressures involved. Participants examine the role of gravity, degeneracy pressure, and fusion in the context of stellar evolution and collapse.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the formation of neutron stars, suggesting that electrons shrink into their nuclei, prompting a discussion on the causes of this behavior.
  • Another participant explains that gravity balances with outward pressure, which diminishes when a star exhausts its fuel, leading to collapse.
  • Questions arise regarding the nature of the outward pressure, with some suggesting it is related to fusion processes.
  • It is noted that heat from fusion prevents implosion until fuel is depleted.
  • Participants introduce the concept of degeneracy pressure, specifically neutron degeneracy pressure, as a key factor in stabilizing neutron stars against collapse.
  • One participant clarifies that collapse is unrelated to fusion heat, emphasizing that degeneracy pressure is independent of temperature and that accretion from another star is necessary for a neutron star to become a black hole.

Areas of Agreement / Disagreement

Participants express differing views on the nature of outward pressure and its relationship to fusion, with some asserting that degeneracy pressure is the primary stabilizing force. The discussion remains unresolved regarding the specifics of how these pressures interact during the formation of neutron stars.

Contextual Notes

Some claims about the relationship between degeneracy pressure and temperature, as well as the mechanisms of stellar collapse, are not fully explored, leaving room for further clarification and discussion.

madphysics
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Hi guys, I'm not to great at physics and all but I want to learn more. I hope you guys can help me in that aspect.First of all, how do neutron stars form? I was told their electrons shrink into their nucleuses and therefore the whole star shrinks, but what causes the atoms to behave like that?
 
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Gravity.

Stars are balanced between gravity trying to squeeze everything together and some outward pressure trying to push it apart.
When a star runs out of fuel, ie. ends up being made of stuff that dones't give off enough energy in a fussion, there is no outward radiation pressure to push the stuff apart.
In neutron stars the pressure to keep them up comes from degeneracy pressure - basically the neutrons can't be pressed together any tighter.
If the star's gravity is big enough to overcome this it becomes a black hole.
 
What is the outward pressure? It's not inertia like planets. Is it the process of fusion?
 
You got it - heat from fusion keeps the star from imploding...until the fuel runs out.
 
madphysics said:
What is the outward pressure? It's not inertia like planets. Is it the process of fusion?

The outward "pressure" is the Pauli principle
 
The outward pressure is neutron degeneracy pressure. Electron degeneracy pressure is what stops white dwarfs collapsing in but when this is less than the gravitational pressure, inverse beta decay creates neutrons. Neutron stars generally have a radius of (electron mass/proton mass)*white dwarf radius which turns out to be tiny, something like 10km!

Collapse is nothing to do with heat from fusion. Even if the heat from a stable neutron star had run out and it reached a few K, it would not collapse because the degeneracy pressure is not a function of temperature. The only way to make a stable neutron star tip over the edge to a black hole is by accretion from another object like a second star in a binary system.
 
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