Einsteinring

In an Einstein ring ( also Chwolsonring ) is a ring of electromagnetic radiation of a distant object that comes through the effect of gravity a "foreground" Galaxy materialize. The galaxy acts as a gravitational lens. This phenomenon was predicted by Albert Einstein in his General Theory of Relativity.

In a gravitational lens, the observer sees the remote object several times, because the light rays can reach in different ways to it. If the object is precisely behind the lens, the images appear as a ring around the galaxy segments - even under ideal conditions, a complete ring occur.

Theory

The radius of an Einstein ring is called the Einstein radius. In Radian he is

Is

Standing lens and imaged object is not on a line, so instead of Einstein ring several images arise, then the distances between these images is of the order of the Einstein radius. The Einstein radius is so even in this more common case an idea of ​​the extent of the effect produced by the gravitational lens.

For actually observed examples of gravitational lensing is the approximate size of the Einstein radius:

  • Lens galaxy, imaged object distant galaxy: Some tenth arc seconds to a few arcseconds.
  • Lens galaxy clusters imaged object distant galaxy: Some 10 arc seconds.
  • Lens star and object being imaged stars in our Milky Way: about 0.001 arcsec, see also microlensing.

Observations

It can be observed from the Earth only a few Einstein rings because the source of radiation must be exactly behind the gravitational lens. The previously observed Einstein rings, the foreground galaxies are located at distances of several billion light years.

The first Einstein ring (MG 1131 0456 ) was established in 1987 with the VLA recorded (publication 1988). By 2008, more than 70 Einstein rings were found. Many were found in sky surveys, some of which were examined in detail by the Hubble Space Telescope:

SDSS J162746.44 005357.5, diameter 2:08 ± 0.08 "

SDSS J120540.43 491029.3

A double Einstein ring was discovered in 2008. Such a double Einstein ring is formed when at the same time two galaxies are at different distances behind the lens galaxy. The probability of such a situation is at about one to ten thousand. In this case, it was three galaxies at intervals of three, six and eleven billion light years. The geometry of the recorded objects allows conclusions to gravity and thus the mass of the deflecting ( middle ) galaxy, which could be determined to a billion suns:

Other examples

  • B1938 666: Was 1992 by Patnaik et al. discovered as a gravitational lens system. Later, with the " Merlin " (Multi- element Radio Linked Interferometer ), a composite of radio telescopes in the UK and the Hubble Space Telescope, an Einstein ring with this lens discovered (King et al., 1997/1998 ).
  • SDSS J143001.30 410440.6
Gravitational constant Light-year Jodrell Bank Observatory
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