Neutron Star
When a star comes to the end of its life-cycle, its demise is determined by its mass. An average star, like the Sun, will become a white dwarf star. More massive stars have a more violent end in store for them: a crushing gravitational collapse followed by a supernova explosion.
A neutron star is a stellar corpse remaining after a star has taken the latter path. When the atomic neutron was discovered in 1932, theoretical scientists suggested that if the material in a star could be subjected to high enough pressure, its electrons could be forced into its atomic nuclei, forming a star composed of neutrons. Astronomers Walter Baade and Fritz Zwicky theorized that a Type II supernova explosion could provide that necessary pressure.
The discovery of the first neutron star did not occur until 1967. While investigating astronomical objects with a radio telescope, Jocelyn Bell, a graduate student at Cambridge University, detected a mysterious source that was producing extremely regular, rapid, intense pulses. Under the guidance of Antony Hewish, her professor, Bell located a number of similar sources while Hewish analyzed the data collected. The "pulsating radio sources" were dubbed pulsars. Hewish postulated that the sources might be neutron stars, and once the pulsars had been studied carefully, other astronomers such as Thomas Gold came to agree that they were indeed the "signatures" of neutron stars.
According to a theory put forth by astronomer Subrahmanyan Chandrasekhar in the 1930s, when a massive star with a core greater than 1.4 solar masses runs out of nuclear fuel, a catastrophic "implosion" occurs. Without any radiation pressure to sustain an outward force, the star undergoes a gravitational collapse that crushes its very atoms--its protons and electrons come together to form neutrons. This collapse may occur in less than a second; the core of the star shrinks from about the size of the Earth to a diameter of less than 62 miles (100 km), essentially fusing into a single gigantic nucleus. The outer layers, drawn in by the tremendous gravitational collapse yet energized by a massive burst of neutrinos from the core, explode in a brilliant supernova. The very small, dense neutron core with a radius of about six miles (10 km) is left behind.
Such a compact object spins incredibly rapidly; for example, a neutron star found at the center of the Crab Nebula is rotating at 30 times a second. As the star spins, an intense magnetic field generated by the object sweeps around like a lighthouse beacon, and its pulses can be detected with radio telescopes if they sweep past the earth. This is the source of the pulsing signals first detected by Bell and Hewish.
More than 400 neutron stars have been detected. Some of them pulse in visible light, some pulse in high-energy x-rays. Only the Crab pulsar is detectable at radio, visible, x-ray and gamma ray wavelengths. Of the 400, only three have been found within visible nebulae. It is believed the neutron star lasts about 100 times longer than the amount of time it takes for its nebula to disperse. Just as a star with a core greater than 1.4 solar masses becomes a neutron star, theory suggests that very massive stars with cores greater than 2 to 3 solar masses undergo an even more catastrophic transformation--they become black holes.
In 1992, a neutron star took the astronomical spotlight as researcher Alexander Wolszczan discovered a pair of planets orbiting it. These planets were hailed as confirmation of the existence of extrasolar planets, although with such a beast for a parent star, they would hardly be hospitable to humans.
This is the complete article, containing 597 words
(approx. 2 pages at 300 words per page).
