Berlin 2005 – scientific programme

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GR: Gravitation und Relativitätstheorie

GR 14: Gravitation im Universum

GR 14.3: Invited Talk

Tuesday, March 8, 2005, 11:45–12:30, TU BH262

Gravitational Lensing as a Powerful Astrophysical Tool: MACHOs, Multiple Quasars and Einstein Rings — •Joachim Wambsganss — Astronomisches Rechen-Institut und Universität Heidelberg, Heidelberg

In 1919, the deflection of light was measured at the solar limb during a total eclipse. This detection quantitatively confirmed the prediction of General Relativity (and initiated Einstein’s fame). In 1979, the first phenomenon of a "double quasar" was detected and explained as an optical illusion, a consequence of strong light deflection by gravity. In the 25 years since, many more gravitational lensing phenomena have been discovered, e.g. giant luminous arcs: highly distorted images of background galaxies; microlensing: time-variable magnification background sources due to intervening stars or dark matter objects ("MACHOs") along the line of sight. Even a few "Einstein rings" were discovered, circular images of background galaxies which occur for perfect alignment between lens and source. Weak lensing has been used for measuring the total mass and the mass distribution in galaxy clusters, and "cosmic shear" measurements are currently being refined in order to get better constraints to the cosmological model.

In the talk, the basics of gravitational lensing are explained with many illustrations, the current state-of-the-art in astrophysics and cosmology is demonstrated, and occasional historic reminiscences are intermingled, in particular regarding Einstein’s contributions.