For a second time, the Nobel Prize in Physics for 1993 was awarded to the discovery of a burnt-out star remnant known as a pulsar. Awarding the Prize to Russell Hulse and Joseph Taylor not only rewarded their discovery of two pulsars dancing around each other but also acknowledged their discovery of a space laboratory that could test one of Albert Einstein's most important theories.
According to Einstein's general theory of relativity of 1916, the Universe exists in three-dimensions plus time as a fourth dimension. This space-time, as it is commonly known, behaves much like a liquid, being distorted by the presence of massive bodies, such as stars, and forming ripples of gravitational radiation as these bodies move through the cosmos. Finding these predicted ripples in the fabric of space-time proved difficult as it required locating an object large enough and travelling fast enough through space to create gravitational waves that can reach Earth before fading away.
In the same year that Antony Hewish received the 1974 Nobel Prize in Physics for his role in the discovery of a pulsar - the collapsed and superdense corpse of a massive star, known as a neutron star, that is left behind when it dies in a supernova explosion - Joseph Taylor and his student Russell Hulse discovered a pair of pulsars that are close enough together to orbit around each other in space. Since this so-called 'binary pulsar' is moving fast and the two stars are close together, Einstein's theory predicted that they should generate significant amounts of gravitational radiation, which in turn steals energy from the two pulsars, making them spiral slowly towards each other. After four years of meticulous observations Taylor showed that Einstein's theory passed all tests: the two pulsars are not only spiralling towards each other, but they are doing so at almost exactly the rate predicted by the theory.
Hulse and Taylor's observations, although indirect, provided the strongest proof yet for gravitational radiation. Their findings have provided the impetus to develop a series of gravity-wave detectors, which aim to catch gravitational radiation from astronomical phenomena like black holes or two merging neutron stars through more direct means, as their passing waves wash over Earth.