X-ray binary

X-ray binaries are a class of <a href="/facts/Binary_star/TYlDe1bD">binary stars</a> that are luminous in <a href="/facts/X-ray/wseP79cN">X-rays</a>. 
The X-rays are produced by matter falling from one component, called the donor (usually a relatively common <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> <a href="/facts/Star/PFbd6ICx">star</a>), to the other component, called the accretor, which can be a <a href="/facts/White_dwarf/gIYlTtrC">white dwarf</a>, <a href="/facts/Neutron_star/4enfoxBA">neutron star</a> or <a href="/facts/Black_hole/1r2lmkcF">black hole</a>. 
The infalling matter releases <a href="/facts/Gravitational_energy/SJpNw6G5">gravitational potential energy</a>, up to 30 percent of its rest mass, as X-rays. (Hydrogen <a href="/facts/Nuclear_fusion/hP0gLDqj">fusion</a> releases only about 0.7 percent of rest mass.) The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation.
An estimated 1041 <a href="/facts/Positron/HgV4zBzA">positrons</a> escape per second from a typical low-mass X-ray binary.

X-ray binary open-in-new

X-ray binary