16 jan. 2018 Gravitational lensing is predicted by Albert Einstein's theory of general relativity.

Einstein ring

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In observational astronomy an Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring, is the deformation of the light from a source (such as a galaxy or star) into a ring through gravitational lensing of the source's light by an object with an extremely large mass (such as another galaxy or a black hole).^[1][2] This occurs when the source, lens, and observer are all aligned — a syzygy. The first complete Einstein ring, designated B1938+666, was discovered by collaboration between astronomers at the University of Manchester and NASA's Hubble Space Telescope in 1998.^[3]

Contents

• 1 Introduction
• 2 History
  • 2.1 Known Einstein rings
• 3 Extra rings
  • 3.1 A simulation
• 4 See also
• 5 References
  • 5.1 Journals
  • 5.2 News
• 6 Further reading

Introduction

Gravitational lensing is predicted by Albert Einstein's theory of general relativity. Instead of light from a source traveling in a straight line (in three dimensions), it is bent by the presence of a massive body, which distorts spacetime. An Einstein Ring is a special case of gravitational lensing, caused by the exact alignment of the source, lens, and observer. This results in a symmetry around the lens, causing a ring-like structure.

The geometry of a gravitational lens

The size of an Einstein ring is given by the Einstein radius. In radians, it is

${\displaystyle \theta _{E}={\sqrt {{\frac {4GM}{c^{2}}}\;{\frac {d_{LS}}{d_{L}d_{S}}}}},}$

where

${\displaystyle G}$ is the gravitational constant,

${\displaystyle M}$ is the mass of the lens,

${\displaystyle c}$ is the speed of light,

${\displaystyle d_{L}}$ is the angular diameter distance to the lens,

${\displaystyle d_{S}}$ is the angular diameter distance to the source, and

${\displaystyle d_{LS}}$ is the angular diameter distance between the lens and the source.

Note that, over cosmological distances ${\displaystyle d_{LS}\neq d_{S}-d_{L}}$ in general.