The first pulsar was jokingly labelled a signal from little green men
In 1967 graduate student Jocelyn Bell noticed a strange, perfectly regular radio signal ticking every 1.337 seconds. Nothing like it had ever been recorded, and she and her supervisor half-seriously nicknamed it LGM-1, for little green men. A second source elsewhere in the sky soon killed the alien theory.
Bell spotted the signal in data recorded on August 6, 1967, by a new radio telescope she had helped build at Cambridge. Her supervisor, Antony Hewish, first took it for interference, but it always came from the same patch of sky, ruling out anything on Earth. A fast chart recorder in November resolved it into evenly spaced pulses. Bell later described the dilemma of how anyone could responsibly announce possible evidence of life elsewhere. Her discovery of another pulsing source on December 21 settled the matter: these were natural objects. The original is now catalogued as PSR B1919+21.
A pulsar is a rotating, intensely magnetised neutron star that sweeps beams of radiation from its magnetic poles. Like a lighthouse, it is visible only when a beam points at Earth, which produces the pulses. Walter Baade and Fritz Zwicky had proposed neutron stars in 1934 as the dense leftovers of supernovae, and Franco Pacini suggested in 1967 that a spinning, magnetic one would radiate. The Crab Pulsar, found in 1968 at the heart of the Crab Nebula with a 33-millisecond period, clinched the model, since nothing else could flash that fast.
In 1974 Hewish shared the Nobel Prize in Physics with Martin Ryle, the first astronomers so honoured. Bell was left out, a decision that stirred lasting controversy, though she has said she feels no bitterness. That same year Russell Hulse and Joseph Taylor found a pulsar orbiting another neutron star every eight hours; its slowly shrinking orbit gave the first evidence of gravitational waves and won them the 1993 Nobel.
Millisecond pulsars, discovered in 1982 with a specimen spinning about 38,500 times a minute, keep time rivalling the best atomic clocks. And in 1992 Aleksander Wolszczan found the first planets beyond the Solar System orbiting a pulsar, though its fierce radiation makes life there very unlikely.
Source: Pulsar
