A pulsar is a neutron star whose magnetic axis is not aligned with the rotational axis. As a result, charged particles which accrete in a disk orbiting around the star's equator are ejected along the magnetic poles, sweep across the sky, and in a very few cases can be detected from Earth as regular pulses in the radio frequency spectrum. Very often these pulses are spaced only a few milliseconds apart, indicating the incredible rotational speed of the pulsar.
In 1974 University of Massachusetts astronomer Joseph Taylor and his graduate student Russell Hulse discovered two pulsars in a very eccentric orbit around each other with a period of 7.75 hours. Over the course of twenty years, their observations of the star's periastron advance (analogous to the perihelion advance of Mercury but a much larger effect) as well as the increase in the orbital period was cited as evidence for General Relativity, when in fact the observations were merely shown to be consistent with theoretical predictions provided that certain assumptions were made about the masses of the pulsars and other physical attributes to fit the data to the theory. Nevertheless, the two researchers were awarded the 1993 Nobel Prize in physics.
- David Darling. Gravity's Arc, 2006, John Wiley & Sons