Black holes

For stars larger than about 30 solar masses, not even the neutron degeneracy pressure of neutron stars can balance the intense gravitational forces. In this case the star collapses completely, leaving what is known as a black hole. A black hole is an object so dense that not even light can escape from it.

Of course, by their nature, black holes are difficult to detect. However, some binary star systems are candidates which may show that black holes do exist. Binary star systems are two stars rotating amongst each other. There are a couple of cases seen, however, where one twin star is invisible, but the visible star appears to be rotating about something. This typically is accompanied by a flow of material from the visible twin into what looks like a void. This behaviour is taken as indirect evidence for the invisible twin being a black hole.