Binary stars are pairs of stars sufficiently close to each other to be held together by their mutual gravitational attraction (like the Earth and the Moon), revolving in orbit around their common centre of gravity. Such pairs of stars are exceedingly common throughout the Universe.
If, however, one of these stars collapses and becomes a compact object, like a neutron star or a black hole, its huge gravitational field, will cause matter to be drawn from the surface of its companion star sweeping it around into an accretion disk. The matter of this disk spirals faster and faster towards the centre and by dynamic friction reaches very high temperatures (typically 10 000 000 K), thus emitting X-rays and gamma-rays. There is still no definite proof that black holes exist, although there are many indications that black holes are a reality.
Many interacting binaries are thought to be black hole candidates, as their supposed masses seem to be greater than the mass attributed to neutron stars. One expects binaries to behave differently according to whether the compact object is a neutron star or a black hole. Thanks to the greatly improved observational instruments used by INTEGRAL, astrophysicists hope to be able to distinguish one from the other through their gamma-ray emissions, thus, proving the existence of black holes.
Last Update: 18 Mar 2008