What is a neutron star?

A neutron star is an incredibly dense and compact remnant of a massive star that has ended its life in a supernova explosion. When a star much more massive than our Sun exhausts its nuclear fuel, its core collapses under gravity. If the remaining core’s mass is between about 1.4 and 3 times the mass of the Sun, the collapse is halted by neutron degeneracy pressure, resulting in the formation of a neutron star. Neutron stars are composed almost entirely of neutrons—subatomic particles with no electric charge. Due to their extreme density, a neutron star packs about 1.4 times the mass of the Sun into a sphere only about 20 kilometers (12 miles) in diameter. This means a sugar-cube-sized amount of neutron star material would weigh around a billion tons on Earth. Neutron stars also often have very strong magnetic fields and can rotate extremely rapidly, sometimes hundreds of times per second. These rotating neutron stars are observed as pulsars, emitting beams of electromagnetic radiation detectable from Earth. In summary, a neutron star is the ultra-dense core left behind after a massive star explodes, offering fascinating insights into matter under extreme conditions and the life cycles of stars.