A binary pulsar, a rotating neutron star that generates regular pulses of radiation, exists in a binary system in which the pulsar has a companion stellar object (e.g., another neutron star, white dwarf or a main-sequence star). In binary systems both stellar bodies orbit around a common center of mass.

Most solitary pulsars have periods of around one-half second. Approximately two to seven percent of pulsars, however, have shorter periods on the order of milliseconds (millisecond pulsars). The period of normal pulsars increases with age, resulting in a corresponding decrease in the magnetic field, such that after 107 years the radio emission is undetectable. The slowdown rates of millisecond pulsars are extremely small, indicating a lifetime of 109 years. Such pulsars are clearly a population separate from normal pulsars. That pulsars are part of a binary system is indicated by Doppler shifts in the pulse period and...