Astronomers dissect a gigantic black hole with the Einstein Cross

December 13th, 2008 - 3:35 pm ICT by ANI  

Munich, Dec 13 (ANI): Astronomers have used the ESOs (European Southern Observatorys) Very Large Telescope, along with a double natural magnifying glass known as the Einstein Cross, to scrutinize the inner parts of the disc around a supermassive black hole 10 billion light years away.

The Einstein Cross, a famous cosmic mirage, is a cross-shaped configuration consisting of four images of a single very distant source.

The multiple images are a result of gravitational lensing by a foreground galaxy, an effect that was predicted by Albert Einstein as a consequence of his theory of general relativity.

The light source in the Einstein Cross is a quasar approximately ten billion light-years away, whereas the foreground lensing galaxy is ten times closer.

The light from the quasar is bent in its path and magnified by the gravitational field of the lensing galaxy.

This magnification effect, known as macrolensing, in which a galaxy plays the role of a cosmic magnifying glass or a natural telescope, proves very useful in astronomy as it allows us to observe distant objects that would otherwise be too faint to explore using currently available telescopes.

The combination of this natural magnification with the use of a big telescope provides us with the sharpest details ever obtained, explained Frederic Courbin, leader of the programme studying the Einstein Cross with ESOs Very Large Telescope.

The microlensing affects various emission regions of the disc in different ways, with smaller regions being more magnified.

Because differently sized regions have different colours (or temperatures), the net effect of the microlensing is to produce colour variations in the quasar images, in addition to the brightness variations.

By observing these variations in detail for several years, astronomers can measure how matter and energy are distributed about the supermassive black hole that lurks inside the quasar.

Astronomers observed the Einstein Cross three times a month over a period of three years using ESOs Very Large Telescope, monitoring all the brightness and colour changes of the four images.

Thanks to this unique dataset, we could show that the most energetic radiation is emitted in the central light-day away from the supermassive black hole and, more importantly, that the energy decreases with distance to the black hole almost exactly in the way predicted by theory, said Alexander Eigenbrod, who completed the analysis of the data. (ANI)

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