A Neutron Star is a mass entirely of neutrons the result of Gravitational Collapse of a star after it has used up the energy to resist such collapse. Its mass is large enough that Gravity overcomes Electron Degeneracy and causes such collapse but not so large as to overcome their internal pressure which prevents them collapsing into a Black Hole (Neutron Degeneracy Pressure). Typical mass is 1.4 to 3.2 solar masses with a radius on the order of 10 km. Stars with lesser mass become White Dwarves instead.
Their existence was first proposed in 1934 and candidates were identified in the 1960s that have panned out.
Rotation of neutron stars and their Magnetic Field makes them pulse (Pulsars). The magnetic field may be strong enough to affect the trajectory of Accretion, channeling it to the magnetic poles. The point where the magnetic field is sufficiently strong to overcome the accreting mass's Kinetic Energy is called the Alfvén Radius.
Black Widow Pulsar (B1957+20)
Calcium-rich Gap Transient
Canadian Institute for Theoretical Astrophysics (CITA)
Fast Radio Burst (FRB)
Gamma-Ray Burst (GRB)
Crab Nebula (M1)
Hulse-Taylor Binary (PSR B1913+16)
Supernova Remnant (SNR)
Tolman-Oppenheimer-Volkoff Limit (TOV)