Neutron Star
An ultradense stellar core remnant produced by the core-collapse supernova explosion of a massive star, composed almost entirely of neutrons.
Governing formula
M ≈ 1.4–2.1 M_☉, R ≈ 10–12 km, ρ ≈ 10¹⁷ kg/m³
SI unit
M_☉ (Mass), km (Radius)
In depth
When core mass exceeds the Chandrasekhar limit (1.4 M_☉), gravitational pressure forces electrons and protons to combine into neutrons. Gravitational collapse is halted by neutron degeneracy pressure at nuclear densities (~10¹⁷ kg/m³).
Examples in the real world
The Crab Nebula neutron star spinning 30 times per second at the center of the 1054 AD supernova remnant.