neutron star

A gravitationally compressed stellar core, made almost

entirely of neutrons. They are formed in supernova explosions, when a

massive star (8 to 20 times the mass of the Sun) runs out of fuel and

collapses upon itself, or when a white dwarf accumulates too much

material from a binary companion, exceeds the Chanrdasekhar mass,

and collapses. The force of gravity squeezes protons and electrons

together to form neutrons. Since neutrons are electrically neutral and

don't repel each other like protons do, neutron star densities are

extremely high: 10^14 grams/cubic centimeter, or 100 trillion times as

dense as water. A full bathtub of neutron star (instead of water)

would weigh as much as two Mt. Everests. A neutron star with the same

mass as the Sun is between 10 and 15 km (6-10 miles) wide, with a

liquid neutron core and an atmosphere of iron. Some neutron stars,

called pulsars, spin rapidly at speeds of 1 to 1000 revolutions per

second and sustain a powerful magnetic field, which produces radio

pulses which can be detected with radio telescopes.