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Searching for Extrasolar Planets with Gravitational Microlensing: Challenges and Exciting Results

Kolloquium Fachbereich Physik

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Abstract:

The first planet around a solar-type star was discovered in 1995, since then „extrasolar planets“ has developed into a highly exciting and booming field in Astrophysics. Astronomers employ six different techniques in order to search for exoplanets, all based on very simple physical principles. Gravitational microlensing is one of those, it is particularly sensitive to low mass planets and is ideally suited for statistical analyses of the abundance of exoplanets in the Milky Way. After a short description of all search techniques, in the talk the basics of microlensing and its mode of operation will be explained, as well as its advantages and disadvantages compared to other planet-search methods. About 60 exoplanets have been discovered so far by microlensing surveys. A statistical analysis on the Galactic abundance of (bound and possibly unbound) exoplanets will be presented and discussed, with particular emphasis on the result that “Planets are the rule, not the exception”: Abundances analyses based on microlensing show that on average every Milky Way star has at least one planet! Exciting new results will be presented on „parallax measurements“ of microlensing events. In a brief outlook, the immense potential of gravitational microlensing for detections of Earth- and Mars-mass planets, of exomoons and of free-floating planets will be highlighted.