Cosmic Einstein Cross under the Gravity Magnifying Glass

First information about the environment of the supermassive black hole in the center of the quasar

"Einsteinkreuz" in the constellation Pegasus © ESO / F. Courbin et al.
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A galaxy in front of him distorts the light of the quasar Q2237 + 030 so that it forms a cross of five bright stars, the "Einsteinkreuz". For the first time, astronomers have used this gravitational lens to gain more detailed information about the nearby environment of the quasar and the black hole at its center.

The "Einstein Cross" is a phenomenon in the constellation Pegasus, which resembles a cross with its four bright points of light and a central spot. In reality, however, it hides behind only a single source of light, a quasar located about ten billion light-years from Earth. The strange distortion and multiplication of his light he owes to a so-called gravity lens, a line of sight in front of him galaxy, whose gravity deflects the quasar light.

The ingenious physicist Albert Einstein had already predicted precisely this effect of the space-time structure as a consequence of his general relativity theory. Today, the gravitational lensing phenomenon is one of the commonly used methods in astronomy of deep space. Because the lens effect of heavy objects in the foreground not only distorts the light of distant stars, it also amplifies it and thus facilitates the observation. In addition to the effect of whole galaxies, the individual stars also change the "lens" image in it. Their movement makes the distorted images look brighter sometimes darker.

Brightness changes reveal details about Quasarum field

An international team of astronomers used this method to study the famous Einstein Cross. By observing the brightness variations of the distorted images over three years using the Very Large Telesope (VLT) of the European Southern Observatory, they were able to determine how matter and energy is distributed around the supermassive black hole that sits inside the quasar.

"The combination of its natural magnification and the use of a large telescope gave us the sharpest details ever received, " explains Frédéric Courbin, project manager at ESO Telescope. The scientists achieved a resolution of one millionth of an arc-second, the size of a euro coin five million kilometers away. display

Closeup of the "Einstein Cross" ESO / F. Courbin et al.

First direct measurement of the accretion disk

"Thanks to this unique data, we were able to show that the highest-energy radiation from a radius of one day of light emanates from the supermassive black hole, " explains Alexander Eigenbrod from the Polytechnic University of Lausanne. "And, more importantly, the energy increases with the distance to the black hole to the extent predicted by the theory."

So far, there have been no direct and model-independent observations that have allowed researchers to resolve or confirm the various theories that exist on the formation of quasars. "This is the first accurate and direct measurement of the size of the accretion disk of a quasar at a wavelength independent of the models, " says project researcher Georges Meylan. In the light of the new data the theories can now be checked.

(ESO, 16.12.2008 - NPO)