pulsar stars were discovered by accident, when Bell and Hewish were looking for twinkling sources of radio radiation. The explanations from the radio pulses proved the existence of neutron stars, incredibly dense remains of massively collapsed stars. Bell and Hewish were tracking the twinkling sources of radiation using a radio telescope. The telescope produced around 30 meters of chart paper each day, the data was then analysed by Jocelyn Bell. She quickly learned to recognise scintillating sources. But two months into her observations Bell became aware of a bit of scruff on the records. The new signal didn't look like it came from any scintillating source or a man made source. When Bell checked back on the records she found the scruff had occurred before, but always from the same patch of sky. This strange new signal deserved more attention so Bell starting making faster chart recordings on the area the signal had appeared. For weeks she found nothing, then finally at the end of november the signal appeared on the fast recording. the scruff was a series of pulses equally spaced and 1.3 seconds apart, 1.3 seconds is far to fast for a pulsation rate for something as large as stars so this regular signal must be man made. But when Hewish checked the records he found the position of the source meant it must be coming from outer space. Hewish and Bell considered various explanations, it wasn't radar reflected from the moon, also it wasn't a strange satellite of course. It wash't equipment failure because another telescope had also picked up the signal. Calculations showed it was well out of the solar system as well. The team measured the duration of the pulses and they found the time was only 16 milliseconds. The short duration suggested the source could be no larger than a small planet. If the radio waves were coming from another planet their frequency would shift as the planet orbited the alien sun. The frequency would be higher when it would be coming towards us and lower when it moves away. Hewish made measurements to see if the signal could come from another planet, but the measured changes were only there due to the movement of our own planet around the sun. The radio astronomy group were not sure as to how to publish their discovery. It seemed highly unlikely that the signals came from aliens but no one had a better answer. If the team had discovered alien life, who should they tell first. Bell was quite annoyed that the supposed aliens had chosen his telescope, his frequency. But when bell returned to his analysis he found another scruff in a completely different part of the sky. Bell went out to the telescope that night and found it was another pulsing signal, slightly faster with pulses every 1.2 seconds. Now she was reassured that the pulses had some natural explanation, its very unlikely that two lots of aliens would both choose the same telescope at the same time trying to signal the same planet. By January Bell and Hewish had discovered 4 of these pulsing sources . They wrote a paper describing the source and sent it to journal nature, where it was published on the 24th February, 1968. Thus pulsar stars were discovered.
when a star collapses on itself it ether produces a neutron star, a black hole, a dwarf star or a pulsar star
