  Binary radio pulsars, first discovered by Hulse and Taylor in 1974 [1], are a
unique tool for experimentally testing general relativity (GR), whose validity
has been confirmed with a precision unavailable in laboratory experiments. In
particular, indirect evidence of the existence of gravitational waves has been
obtained. Radio pulsars in binary systems (which have come to be known as
recycled) have completed the accretion stage, during which neutron star spins
reach millisecond periods and their magnetic fields decay 2 to 4 orders of
magnitude more weakly than ordinary radio pulsars. Among about a hundred known
recycled pulsars, many have turned out to be single neutron stars. The high
concentration of single recycled pulsars in globular clusters suggests that
close stellar encounters are highly instrumental in the loss of the companion.
A system of one recycled pulsar and one 'normal' one discovered in 2004 is the
most compact among binaries containing recycled pulsars [2]. Together with the
presence of two pulsars in one system, this suggests new prospects for further
essential improvements in testing GR. This paper considers theoretical
predictions of binary pulsars, their evolutionary formation, and mechanisms by
which their companions may be lost. The use of recycled pulsars in testing GR
is discussed and their possible relation to the most intriguing objects in the
universe, cosmic gamma-ray bursts, is examined.
