Are there any amount of protons, electrons and other subatomic particles inside neutron stars?
I wonder if there are protons or electrons inside neutron stars trapped by their gravity and degeneracy pressure...How many electrons/protons are there if so?
I agree with the other answers, there are protons and electrons in neutron stars, and their numbers are quite significant:
a neutron star is not entirely composed of neutrons. It also contains some number of protons and electrons (probably about 10% each of the number of neutrons). It is those particles, which are electrically charged, that can produce currents and therefore sustain a magnetic field.
Cole Miller
EDIT (Jan 7,2023): Another reference (https://doi.org/10.1038/s41586-018-0400-z):
Neutron stars contain about 5%–10% protons and electrons in their central layers.
There are indeed a number of protons in neutron stars. However, to achieve charge neutrality, there must be an equal number of electrons. Energies for these occupied electron states increase much more rapidly than neutron states. Bearing in mind the exclusion principle, this means that (unlike everyday conditions) a proton and electron can be associated with a higher energy state than a neutron. Above a very small concentration of protons it becomes energetically favourable for electron capture to convert the protons to neutrons.
Edit: To obtain a rough estimate of the ratio of protons/electrons to neutrons, assume that the Fermi energy of the electrons and neutrons is equal (the protons themselves will make a negligible contribution). The Fermi energy for a mass $m$ species can be estimated as: $$ E_F = \frac{\hbar}{2 m} \left ( \frac{3 \pi^2 N}{V} \right )^{2/3} . $$ As the electron is about $1840$ times as massive as the electron, there will be about $1840^{3/2} \approx 78800$ times as many neutrons as protons/electrons.
The above assumes that Fermi energy is much larger than the mass-energy difference between the neutron and a proton-electron pair. It is also assumed that this energy is much lower than mass-energy difference compared with exotic baryon-lepton pairs. This is not necessarily true of neutron star cores, where strange matter is predicted. Finally, it is assumed that the particles are non-interacting.
There should be, yes. Neutrons naturally beta decay to protons, electrons and antineutrinos. If you had pure neutron matter, some neutrons would decay. But if the electron pressure is high enough, this decay mode is suppressed. So we think that neutron star interiors have an adequate electron density to provide the necessary pressure, and adequate proton density for charge neutrality.
