Why are there only neutrons in a neutron star?

Answer 1

Neutron stars are composed (mostly) of neutrons because during the star's life, the fusion processes strip apart atoms, leaving the electrons behind inside the star's core. When the star runs out of fuel and fuses up the atomic chain and hits nickel, it collapses. The pressure from the collapse is enough to force all those electrons together and as you compress them more and more, the free protons from the fusion processes bond with the electrons, forming neutrons.

Put simply, it's mostly neutrons because it's just doesn't have enough mass to be made of mostly quarks or become a singularity.

Answer 2

Neutron stars are extremely dense remnants of stellar explosions. The intense gravitational forces in a neutron star compress the atomic nuclei to such an extent that electrons are forced into the nuclei, combining with protons to form neutrons. This results in a star composed almost entirely of neutrons.