What Makes Neutron Stars So Unique?

[Astronuc]

As for emission lines, you usually don't get those in stars unless there is a significant extended region of hot gas beyond the star's photosphere. Stars with heavy stellar winds or interacting binaries will sometimes have emission lines, but most of the time, the spectrum is thermal+absorption. Isolated neutron stars that we can see are usually very hot, so the gas is too heavily ionized even for absorption lines (at least in the optical and UV).

I would imagine it's just gamma radiation - there are no atoms in the core of a neutron star. Highly ionized atoms would produce mostly (if not completely) X-rays.

'Neutronium' is an example of degenerate matter. The link has a rather interesting discussion of 'isotopes of neutronium', although there is a comment that the actual form of neutronium is not well understood.

Neutronium is a colloquial and often misused term for an extremely dense phase of matter that occurs under the intense pressure found in the core of neutron stars and is currently not well understood. It is not an accepted term in astrophysics literature for reasons which will be explained below, but is used with some regularity in science fiction . . . .

 

[SpaceTiger]

I would imagine it's just gamma radiation - there are no atoms in the core of a neutron star.

We don't see the core of the neutron star, we see the surface. On the surface, there are indeed highly ionized atoms and degeneracy is negligible

Highly ionized atoms would produce mostly (if not completely) X-rays.

Not really, the energy of the radiation that comes out depends largely on the temperature. In the case of a neutron star, all but the very youngest have temperatures <10⁶ K, corresponding to a blackbody peak at <100 eV. Some neutron stars do emit a lot in the X-rays, but there are many cases of highly-ionized media (like HII regions) in which the majority of the radiation is in the optical or UV.

 

[Astronuc]

We don't see the core of the neutron star, we see the surface. On the surface, there are indeed highly ionized atoms and degeneracy is negligible

Not really, the energy of the radiation that comes out depends largely on the temperature. In the case of a neutron star, all but the very youngest have temperatures <10⁶ K, corresponding to a blackbody peak at <100 eV. Some neutron stars do emit a lot in the X-rays, but there are many cases of highly-ionized media (like HII regions) in which the majority of the radiation is in the optical or UV.

I was thinking that there has to be a lot of Compton scattering of gamma radiation, hence there would be a fair amount of X-rays. It is true that 100 eV would be in ultraviolet. I suppose there is a distribution of temperature depending on distance from the region of degenerate matter.

At what distance/radius is the region of atomic matter from the degenerate matter? Is there an abrupt transition?

I believe Chronos has indicated that a sufficient model of a neutron star does not exist at this time.

Atoms with most or all of their electrons stripped and roaming free.

Dpes this not imply energies (temperatures) > 100 eV?