Illustrations of a gaseous material falling into a black hole which spirals around to form a flattened accretion disc. The white/yellow areas of the accretion disc indicate the gaseous material heating up as it circulates the black hole. The centre of the disc, close to the black hole, contains a region of very hot electrons, with temperatures of around a billion degrees, known as the corona which produces high-energy X-rays that stream out into space. The corona is the bright region over the black hole, changing in size and brightness.