Research

Two invisible components, dark energy and dark matter, make up most of the energy content of the Universe and yet we know very little about either. As far as we know, dark matter cannot be observed directly. In order to study its distribution in the Universe, we use a technique called gravitational lensing. As predicted by Einstein’s general relativity, mass curves spacetime. Consequently, light rays are differentially deflected in a gravitational potential. If there is a structure along the line of sight between an observer and a distant object, a perturbation in the photon trajectory is caused. As a consequence, the position of the image of the source will be slightly shifted and magnified, and, if extended, it will also be distorted. more

Why are clusters of galaxies interesting objects?

Clusters of galaxies are the largest gravitationally bound structures in the Universe and — according to hierachical structure formation scenario — the latest structures to form. Their masses can exceed 1015 solar masses, and galaxies move within them with up to ~1500km/s.

Clusters are mostly identified in the optical by their galaxy overdensities; the richest clusters contain thousands of galaxies. Whereas the galaxy component of clusters is most easily visible, their dominant mass component is dark matter. In addition there is also smoothly distributed intracluster gas heated up to ~106K, which emitts Bremsstrahlung in Xray-frequences and also changes the energy spectrum of microwave background photons traversing them by the inverse Compton effect. more

Our universe is not completely homogeneous. Instead, the distribution of galaxies when looked at on large scales is a web-like structure where massive and highly overdense knots of galaxies (galaxy clusters) are interconnected by mildly overdense streams of galaxies (galaxy filaments). The evolution of this cosmic web is however largely dominated by the dynamics of dark matter. Gravitational lensing enables us to directly probe all components of the matter density field and to thereby study the laws of gravitational collapse on cosmological scales. more

Galaxy clusters are one of the largest gravitationally bound structures in the universe. more

The field of extrasolar planets, in short exoplanets, is relatively new and one of the fastest-growing branches in astronomy. Over the past decade, advances have been made with a continually rising number of exoplanet discoveries and the more accurate study of their properties. We are using two distinct methods for the detection of such planets. The by far most successful detection technique is the transit method which contributes several thousands of discoveries to the total number of known planet systems. Additionally, we have worked on several radial-velocity surveys which study the Doppler motion of stars in order to detect high-mass planets. Since the number of known systems is now high enough, statistical assessments can be made to make predictions about their formation and properties. more

We study the M31 galaxy to understand the dynamics, composition (dust, Novae, Cepheids, LBVs), and stellar evolution of their components. In particular, we monitor the galaxy to find variable sources and measure their light curves. A very small fraction of these are microlensing events caused by stars in bulge or disk, or compact objects (MACHOs) in the halo whose MACHO content we want to determine. We identify cepheids and analyze their period-luminosity ratios in the optical (PanSTARRS, WWFI) and NIR (HST-data, 3KK) to compare them with theoretical models and to establish M31 as a distance anchor for local Hubble constant determinations. For this purpose, we have also identified further eclipsing binaries for an independent distance determination of M31. more

The Optical and Interpretative Astronomy group at MPE investigates the evolution of cosmological structures ranging from small to large scales, with special focus on: formation and evolution of galaxies, as well as their large scale distribution, characteristics of supermassive black holes, origin and properties of the dark components of the universe, i.e. dark matter, dark energy. more