Active Galactic Nuclei











Image: An artist's impression of the accretion disc around the supermassive black hole that powers an active galaxy. (Image credit: NASA / Dana Berry, SkyWorks Digital)


At the heart of virtually every large galaxy lurks a supermassive black hole with a mass of a million to more than a billion times that of the Sun. Most of these black holes are dormant, but a few per cent are 'active' meaning that they are drawing inwards material from their host galaxy, this forms an accretion disc that feeds the black hole. As the material spirals through the disc it releases vast amounts of energy as heat and light. These active galaxies are the most powerful, continuously emitting sources in the Universe, often more than a hundred billion times more powerful than the Sun. This prodigous luminosity means active galaxies can be seen over huge distance and are among the most distant objects that have ever been detected.

Active galaxies emit radiation over the entire spectrum from radio waves through optical (visible) light up to X-rays and gamma-rays, but are so distant that it is not possible to image the accreion disc or black hole. In order to study active galaxies, and gain a better undertanding of the physics of accretion flows and black holes and how they interact with their host galaxies, we must understand the spectrum of the light and how it changes with time. At Leicester, the programme of observational research into active galaxies makes extensive use of multi-wavelength ground- and space-based observational facilities, several of which include instrumentation built at Leicester. These include using X-ray observations (with ESA's XMM-Newton and NASA's RXTE and Chandra missions) of the X-ray emission to probe the space closest around the black hole, detecting the echoes of light that bounce off the accretion disc using ground-based telescopes, and measuring the 'winds' of gas that is blown off the surface of the disc by the radiation (the 'exhaust' of the accretion process) using ultraviolet and X-ray observations.

For further details of current research click this link.

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