In a neutron star, protons and electrons are densely packed together in a highly compressed state. Neutron stars are incredibly dense objects that form from the remnants of massive stars that have undergone a supernova explosion.
The core of a neutron star is composed primarily of neutrons, hence the name. The intense gravitational forces at the core squeeze protons and electrons together so tightly that they merge to form neutrons through a process called electron capture. In this process, a proton captures an electron, resulting in the transformation of the proton into a neutron and the emission of a neutrino.
As a result, the interior of a neutron star is predominantly composed of neutrons, although there may still be a small number of protons and electrons present. These neutrons are packed closely together, forming a state of matter known as neutronium.
At the surface of a neutron star, where the density is lower, there may be a thin layer called the neutron star crust. In this region, the composition is more complex, consisting of a lattice structure made up of atomic nuclei embedded in a sea of electrons. The crust may contain various elements, such as iron, but it is still significantly denser than any material found on Earth.
Overall, the protons and electrons in a neutron star are mostly transformed into neutrons within the core, while the outer layers may contain a mixture of nuclei and electrons in the crust.