Artist's impression of a binary star system consisting of a black hole (upper right) and a red giant star (upper left). At lower right is a nebula, a cloud of gas and dust where new stars are forming. A stream of gas is being pulled from the atmosphere of the red giant by the immense gravitational field of its companion. As the gas spirals down into the black hole it forms a flat accretion disc which heats up and emits X-rays (bright white spot at centre). For this reason, this type of system is known as an X-ray binary.