When the star expends its nuclear fuel, however, the star collapses under its huge gravitational pull and a black hole is formed. Black holes often seem to be part of binary systems, where the black hole and a visible star revolve around one another. The black hole, with its massive gravitational field, pulls gas from the visible star into itself. When this happens the gas emits strong X-rays which astronomers can detect. Return to circle Neutron Star A neutron star is the core of a star that remains after a supernova explosion.
Neutron stars emit intense X-rays.
At this high pressure electrons and protons combine to form the neutrons of which the star is composed. This name was given for the obvious reason that they emit extremely regular pulses of radio waves. Some pulsars, however, emit visible light, X rays, or gamma rays. The particles give off electromagnet radiation as they are accelerated to near the speed of light. Hence the pulsar swings an electromagnetic radiation beam around the star much like a beacon.