Neutron stars
Gravitationally collapsed cores of massive stars, second only to black holes.
A neutron star is the gravitationally collapsed core of a massive supergiant star, resulting from a supernova explosion and gravitational collapse that compresses the core past white dwarf density to that of atomic nuclei. Surpassed only by black holes, neutron stars are the second-smallest and second-densest known class of stellar objects, with a radius on the order of 10 kilometers and a mass of about 1.4 solar masses. They are thought to number around one billion in the Milky Way, though many have cooled and are difficult to detect; most detected neutron stars are pulsars or part of a binary system.
- radius
- ~10 km (6 miles)
- mass
- ~1.4 solar masses (M☉)
- density
- ~4×10^17 kg/m³ (nuclear density)
- rotation_period
- from about 1.4 ms to 30 s
- escape_velocity
- over half the speed of light
- known_for
- second-densest stellar objects; source of gravitational waves; pulsars
Lore & Background
Once formed, neutron stars no longer generate heat and cool over time, but may evolve through collisions or accretion. They are composed almost entirely of neutrons, supported by neutron degeneracy pressure and repulsive nuclear forces. Newly formed neutron stars may have surface temperatures of ten million kelvins, cooling to around one million kelvins after a thousand to a million years. Their material is remarkably dense: a matchbox-sized amount would weigh about 3 billion tonnes.
Reader's Guide
Neutron stars are central to gravitational wave astronomy. The merger of binary neutron stars produces gravitational waves and is associated with kilonovae and short gamma-ray bursts. Neutron stars also serve as natural laboratories for fundamental physics, as their extreme densities—ranging from nuclei in a sea of electrons in the outer crust to possibly exotic QCD matter in the inner core—allow study of the strong interaction and equation of state under conditions unattainable on Earth. Understanding the nature of matter in neutron star layers and phase transitions remains a major unsolved problem in physics.
Did You Know?
- Neutron stars have an escape velocity of over half the speed of light.
- A matchbox-sized amount of neutron-star material would weigh approximately 3 billion tonnes.
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