In 1967, radio astronomers at Cambridge, England, were astounded to find strange radio signals coming from certain places in space. The signals came in short rapid bursts, or pulses. Each lasted only a few hundredths of a second. However, the pulses repeated with extraordinary regularity. Scientists realized these radio signals were coming from objects sending streams of radiation into space. From Earth, this radiation is seen as short bursts, or pulses. These objects became known as pulsars.

The pulses that astronomers receive from these objects are very sharp. As a result, astronomers conclude that pulsars are very tiny and have a radius of only about 10 miles (16 kilometers). When an object emits a burst of radio-wave radiation, the waves from different parts of the object arrive at the Earth at different times. This causes the original burst of radiation to become blurred. The smaller the object, however, the sharper the burst, or pulse.