Discovery of the Neutron Stars

For decades ,astrophysicists talked about neutron Stars, but ,like the weather ,nobody did anything about them, because nobody could do anything. No known observational technique could detect them and no one could prove they existed. But in November 1967, a 4.5 acre array of radio telescopes in England detected a strange new type of radio source in the sky. Analyzing the surveys , a sharp eyed graduate student, Jocelyn Bell, was astonished to find that one celestial radio source emitted "beeps" every 1.33733 s! At first ,project scientists speculated that they might have actually discovered an artificial radio beacon placed in space by some alien civilization! But further work soon led away from this speculation. By January ,another source was found , pulsing at a different frequency ,arguing against the beacon hypothesis . Analysis showed that the first source was less than 4800 km across,  much smaller than ordinary stars. These pulsing radio sources came to be called pulsars. In February, Anthony Hewish and his colleagues published an analysis suggesting that the pulsars might be superdense vibrating stars that could "throw valuable light on the behaviour of compact stars and also on the properties of matter at high density". The mysterious pulsars turned out to be the long sought neutron stars! In an exciting burst of research, the number of scientific papers on pulsars jumped from zero in 1967 to 140 in 1968. By 1973, about 100 pulsars had been discovered. The codirectors of the original discovery project , Anthony Hewish and Martin Ryle, shared the 1974 Nobel Prize in physics. Why do neutron stars pulse? After collapsing to a small size ,supernova remnant stars have very strong magnetic fields and very fast spins, rotating once every second or so. Ions trapped in the magnetic fields spin around with velocities near the speed of light. In 1968, Cornell researcher Thomas Gold showed how ions trapped in magnetic fields of spinning neutron stars produce strongly beamed radio radiation, so that the pulsar acts like a lighthouse with a beam sweeping around every second. Most pulsars have periods of 1/4 to 13s. The fastest - spinning pulsar found thus far was discovered in 1982 and flashes with a 0.0016s period. It is a mountain-sized ball of nuclear matter that spins 642 times every second (Waldrop, 1983)! The discovery of a pulsar in the center of the Crab Nebula and in other sure nova remnants proves that pulsars are related to supernovae. Careful studies of such pulsars are related to supernovae . Careful studies of such pulsars show that they pulse not only in radio waves but also in X rays and visible light. Neutron stars may have solid crusts ( 1 km thick?)overlying a fluid "neutron soup". Tiny abrupt changes in the spin rates of pulsars have been detected and attributed to "starquake", or fractures in the crust ,which change the mass distribution and hence the rotation rate. It is strange to think of earthquake - like events happening in the solid crusts of star corpses!