How do neutron stars form?
Neutron stars are extremely dense remnants produced by the core collapse of some massive stars. A mass exceeding the Sun's can fit within a region only tens of kilometers across. They are not simply smaller versions of ordinary stars.
Core collapse and dense matter
When pressure support becomes insufficient, the core collapses rapidly. Electron capture contributes to neutron and neutrino production. Quantum properties and nuclear interactions support the resulting dense matter. A neutron star is not simply a uniform ball of free neutrons: its crust and deeper layers differ. The detailed behavior of matter at extreme density remains under investigation.
How are they observed?
Strong magnetic fields and rapid rotation allow some neutron stars to appear as pulsars. Accretion in binary systems can produce X-rays. Mergers can be investigated through gravitational waves and electromagnetic emission. Massive stars do not all leave identical remnants: mass loss, companions, and collapse dynamics matter alongside initial mass, and some collapses produce black holes.