n 1934 Fritz Zwicky and Walter Baade, two astrophysicists in California, proposed a new theory. When a Massive Star reaches the end of its life, its gravity will crush the star and make the core collapse. When this happens a colossal explosion, which they called a Supernova , is triggered. The two speculated that the collapsed core left after a Supernova would be so dense that the protons and electrons in the star would be thrust together and merge into neutrons, forming a Neutron Star.

stronomers of the day readily accepted the concept of the Supernova because they had already witnessed such violent explosions, however the concept of Neutron Stars was more difficult to grasp since they were thought to be unobservable. Physicists at the time calculated a neutron star to have a radii of about six miles (10 kilometers) and a mass of between one and several times that of the Sun. These calculations also showed that Supernovas have a maximum mass of about two to three solar masses.

side from the theoretical model, there was no evidence of the existence of neutron stars and the concept was put on a back burner for the next thirty years. In 1967 a group of English astronomers noticed fluctuating radio signals from distant peculiar galaxies. Jocelyn Bell, who was working with the group, noticed an odd radio signal with a precise pulse rate of one burst every 1.33 seconds. The uniform regularity of the pulses led some astronomers to speculate that they were receiving messages from other civilizations and hence the signal was known informally as LGM-1 (little green men number one). Over the next several months more pulsing radio signals were discovered, which came to be termed pulsars for the uniform regularity of their bursts of radiation.


ith the discovery of other pulsars astronomers focused their attension on peculiar varieties of pulsating stars. Ordinary pulsating stars obey a relation where the pulsation cycle is limited by the star's density. The more dense the faster the cycle. The rates of the first pulsars were consistent with their being White Dwarfs. However, other pulsars were found with drastically shorter cycles which suggested densities much larger than those of White Dwarfs, and astronomers returned to Badde and Zwicky's proposal from 1934 about neutron stars.

alculations of the pulsation period of neutron stars indicated that they should pulsate much faster than any of the pulsars observed. White Dwarfs pulsated too slowly and Neutron Stars too fast to fit the observations. The key to this mystery came from the independent works of two astrophysicists at Cornell University: Franco Pacini and Thomas Gold. Pacini, exploring the link between neutron stars and Supernova remnants, found that a neutron star lingering in the debris of a Supernova could supply large amounts of energy to the surrounding gas if it were rapidly spinning and had a very strong magnetic field. Gold, attempting to explain the rapidity of pulsar pulses, discovered that a pulsar could be a rapidly spinning neutron star, and, as a result of it's magnetic field, could emit radiation in two narrow beams giving the effect of a lighthouse.

he accelerated spinning of neutron stars is explained by the principle called the conservation of angular momentum, simply put this means that any rotating body spins more rapidly as it shrinks. The best example of this are spinning ice-skaters; when they pull their arms in they go from a slow pirouette to a blur.

eutron Stars are also powerful magnets, having a gravitational pull about a trillion times that of the Earth. This is due to their extreme density. The combination of a strong magnetic field and rapid rotation are the cause of the pulsating radiation beams.

he spin of neutron stars and their magnetic fields generate powerful electric fields which rip electrons off the stars' surfaces and accelerate them nearly to the speed of light. These electrons are channeled in two narrow beams by the magnetic field of the star. The emissions created by the acceleration of electrons is called non thermal or synchrotron radiation because its properties are based on the strength of the magnetic field and the acceleration of the electrons rather than the temperature of a heated gas.

pinning objects eventually slow down and pulsars are no exception. However pulsars sometimes speed up suddenly. These jumps are called glitches and can help Astronomers by providing information about the interior of the pulsar. Further study astronomers have discovered that pulsars have three distinct inner regions; a thin gaseous outer atmosphere approximately one millimeter thick, a solid crust several hundred meters thick, and an inner core of liquid neutrons which has remarkable properties such as superfluidity (a state where it can move with virtually no friction. As a result of this superfluid the core can spin at a rate independent of the crust. When the difference in rotation reaches a critical limit the superfluid will shed some of its rotational energy and slow down. The released energy has only one place to go and we observe a glitch where the crust picks up a boost of energy from its core.

s a neutron star slows down its radiation weakens and ultimately becomes undetectable. This is how a neutron star dies, it fades out and become invisible.