X-ray binaries are a class of binary stars consisting in a normal star and a degenerate compact object, a neutron star or black hole. Material is continuously transferred from the normal star (the donor which usually fills its Roche lobe) to the compact object (the accretor). X-ray binaries are called low-mass X-ray binaries (LMXBs) if the donor is less massive than the accretor and high-mass X-ray binaries (HMXBs) if the opposite is true. X-ray binaries are bright sources of X-rays produced by matter falling from the donor to the accretor, and realising gravitational potential energy. The artist impression shows a LMXB composed by an evolved low-mass star, a red giant (the donor), and a neutron star (the accretor). The infalling material form an accretion disk around the neutron star and jets originates from its poles and are collimated by the magnetic field.
Credits: INAF - Osservatorio Astronomico di Palermo.