![]() ![]() ![]() This object lies more than one billion light years away in the direction of the constellation Coma Berenices, and is a Seyfert galaxy, characterised by a very bright AGN resulting from the presence of the massive black hole at its nucleus. Pounds and his collaborators looked at X-ray spectra (where X-rays are dispersed by wavelength) from the galaxy PG211+143. This is particularly relevant to the feeding of supermassive black holes since matter (interstellar gas clouds or even isolated stars) can fall in from any direction. Until now it has been unclear how misaligned rotation might affect the in-fall of gas. In fact, the reason we have summer and winter is that the Earth's daily rotation does not line up with its yearly orbit around the Sun. The orbit of the gas around the black hole is often assumed to be aligned with the rotation of the black hole, but there is no compelling reason for this to be the case. As gas spirals inwards, it moves faster and faster and becomes hot and luminous, turning gravitational energy into the radiation that astronomers observe. Instead it orbits the hole, approaching gradually through an accretion disc - a sequence of circular orbits of decreasing size. However black holes are so compact that gas is almost always rotating too much to fall in directly. With sufficient matter falling into the hole, these can become extremely luminous, and are seen as a quasar or active galactic nucleus (AGN). The centre of almost every galaxy - like our own Milky Way - contains a so-called supermassive black hole, with masses of millions to billions of times the mass of our Sun. As a direct result, gas in-fall - accretion - onto black holes must be powering the most energetic phenomena in the Universe. ![]() They are hugely important in astronomy because they offer the most efficient way of extracting energy from matter. Black holes are objects with such strong gravitational fields that not even light travels quickly enough to escape their grasp, hence the description 'black'. ![]()
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