Neutron stars and black holes in binary systems

Neutron stars and black holes can find themselves with close stellar companions through birth or later accident (section 1). The systems give rise to intense variable X-ray sources and born again pulsars (section 2) and perhaps to still odder things (section 6). They provide the best measurements of neutron star masses and the most persuasive evidence for the existence of black holes in the real world (section 3). Most of the basic evolutionary (section 1) and radiation mechanisms (section 4) required to model the observations have been in place for a decade or more and have survived discovery of new phenomena every couple of years. Many of these involve disks of gas accreting onto the stars (section 5). These disks are perhaps prototypes for those in the cores of quasars. Some problems remain with (a) relative numbers of objects in various evolutionary phases and (b) a few extreme individual systems such as SS 433 and 1957 + 20 (section 6).