Can neutron stars lose energy?

  • #1

Summary:

Since electromagnetic radiation is emitted as electrons decay from higher to lower states of excitation, I would assume that neutron stars cannot lose energy by blackbody radiation

Main Question or Discussion Point

Since electromagnetic radiation is emitted as electrons decay from higher to lower states of excitation, I would assume that neutron stars cannot lose energy by blackbody radiation. That would leave tidal drag and evaporation as the only ways a neutron star can lose energy...True?
 

Answers and Replies

  • #2
DaveC426913
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...and the massive beams of EMR they emit from their poles, by which they were discovered and named 'pulsars'.
 
  • #3
How exactly does a mass of neutrons emit EMR? I thought this emission was from compression of non-degenerate matter as it falls into the neutron star.
 
  • #4
Nugatory
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How exactly does a mass of neutrons emit EMR? I thought this emission was from compression of non-degenerate matter as it falls into the neutron star.
The neutron star is rotating very rapidly and still has its magnetic field, which because of the small radius is very strong. This leads to all sorts of exciting electromagnetic effects.

@DaveC426913 mentioned "pulsars"; the wikipedia article is pretty good.
 
  • #5
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The interior of a neutron star is composed mostly of degenerate neutrons which one would indeed expect to exchange energy via collisions instead of radiation. However, the surface is composed of more ordinary matter (still highly compressed) with electrons and nuclei, and there's nothing preventing these electrons from being bumped up to a higher energy level and then radiating while relaxing to a lower level.
 
  • #6
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The original question appears to have been motivated by the concept of electron degeneracy, which might be applicable to limited regions of a neutron star but is more relevant to white dwarfs. There appears to be an assumption that because the lowest energy levels are all occupied, electrons can't radiate by moving to a lower energy level. However, there are many higher levels of varying energies, and an electron could radiate by moving from a "high" to a "medium" energy level, even if it can't go all the way down to the lowest energy. Thus electron degeneracy is not a barrier to blackbody radiation.
 
  • #7
Thanks, Barakn! Of course the pressure required to collapse ordinary matter will not exist near the surface of a "neutron" star, so ordinary blackbody radiation will be emitted from the surface. I feel silly not to have realized that!
 
  • #8
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Neutron stars can lose a lot of energy by emitting neutrinos. This is supposed to be the way recent formed neutron stars cool quickly.

The small surface area compared to the huge mass makes blackbody radiation not very efficient and only seems to become the dominant way of cooling after temperature dropped a lot.

Neutron stars the part about decline and fall of a neutron star describes these processes in more detail.
 
  • #9
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Summary:: Since electromagnetic radiation is emitted as electrons decay from higher to lower states of excitation, I would assume that neutron stars cannot lose energy by blackbody radiation
Note that this is not how solids, liquids, or even gases at low temperature (non glowing) emit radiation.
The photons will be produced by exciatation of a collection of atoms. Lattice vibrations, or molecule rotation/vibration, or collisions..
 
  • #10
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IIRC, radio-astronomers routinely monitor 'young' neutron stars as they spin-down during their pulsar phase. Usually smoothly, but may have 'timing jumps' due 'star quakes'...
 
  • #11
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Willem2, your comment on different modes of photon creation is appreciated. Keep in mind, though, that the surface temps of young neutron stars are often modeled as being a million Kelvin, and even older ones with surface temperatures close to our sun, so they don't qualify as "low temperature." Their quasi-blackbody spectrum is predominantly in the soft x-ray and ultraviolet range.
 

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