Be X-Ray Binary (2010)
Here is a different kind of x-ray binary. In the foreground (top) is a hot star called a Be star. It
spins so quickly that it is surrounded by a circumstellar disc of matter, flung off via centrifugal
force. The Be star is in orbit around a tiny and powerful neutron star (bottom). While the
individual stars in many binary systems often have circular orbits, in Be x-ray binaries the orbits
are considerably elliptical. When the orbit brings the stars close together, as this image shows,
gas from the Be star's circumstellar disc flows towards the neutron star and surrounds it in a much
smaller accretion disc. This gas is heated to very high temperatures, emitting x-rays. When the
neutron star is far from the Be star, by contrast, it can no longer feed off its companion. Its
accretion disc, and therefore the x-rays, then diminish.
