Neutron stars were first theorized in the 1930s, soon after the discovery of the neutron. In the 1960s, regular radio pulses from space were detected. Their origin was unknown, and some scientists thought these pulses might be evidence of extraterrestrial life. Later, it was discovered that the regular signals were caused by a pulsar, a type of neutron star.
Neutron stars pack 500,000 times the Earth’s mass into a sphere about 12.4 miles (20 kilometers) wide. A teaspoonful of its matter would weigh millions of tons.
Neutron stars form from the death throes of a red supergiant star, such as Betelgeuse. Betelgeuse could have up to 20 times the sun's mass and 1,200 times the sun's radius. When the star explodes, material at the core collapses, creating a neutron star. The neutron star retains the original star's angular momentum, rotating much faster because it is much smaller.
Pulsars are spinning neutron stars that emit a narrow radiation beam. The beam is offset from the pulsar's spin axis, sweeping across space like a lighthouse. As the pulsar rotates, the beam may sweep across the Earth, appearing to astronomers as a flashing object. If the beam does not point in the direction of Earth, it cannot be seen. All pulsars are neutron stars, but not all neutron stars are pulsars.
Magnetars are a kind of neutron star with a powerful magnetic field. The magnetic field is the strongest of any object known (as of 2010) and is powerful enough to distort the shapes of atoms.
Starquakes caused by fracturing of the magnetar's surface can cause huge radiation bursts to be released, which are powerful enough to be detected on Earth, tens of thousands of light-years away.
Magnetars remain active for about 10,000 years, a short time in cosmic history. After that, the magnetar has cooled off and the magnetic energy is dissipated.