Max Planck Institutes and Experts

Spiral galaxies grow by swallowing smaller dwarf galaxies. As they are digested, these dwarf galaxies are severely distorted, forming structures such as surreal tendrils and stellar streams that surround their captors. Now, for the first time, a new survey has detected such tell-tale structures in galaxies more distant than our immediate galactic neighbourhood. This opens up the possibility of testing our current views of galaxy evolution in a new way.

Measurements were made of the velocities of a large number of stars in a young galactic cluster, whose age is only about one million years. The cluster is embedded in the bright emission nebula NGC 3603. It is one of the most massive objects of its kind within the Milky Way. To determine the individual stellar velocities, the astronomers compared the positions of the stars on two images taken with the Hubble Space Telescope ten years apart. From this comparison the motion of hundreds of stars could be determined, showing that the cluster stars have not yet reached a dynamically configuration.

Astronomers have so far found more than five hundred "exoplanets", i. e. planets orbiting other stars. A group of these are large planets with orbits very close to their host stars, the so-called "hot Jupiters". Their mass is similar to our Jupiter but they are often much bigger, indicating that their interior is much hotter. Left to themselves, they should cool down and deflate fairly rapidly to a size similar to the Jupiter in our solar system.

The Lambda CDM model of cosmological structure formation has very successfully matched many observational aspects of the Universe. However, the nature of the main ingredient of this model, the so-called Dark Energy, is currently still a mystery. Scientists at the Max Planck Institute for Astrophysics have recently performed the largest ever computer simulation of cosmic structure formation. Combined with new observational campaigns, this might help to constrain the properties of the Dark Energy and solve one of the most important puzzles in modern cosmology.

eROSITA is the core instrument on the Russian Spectrum-Roentgen-Gamma mission. From 2013 on eROSITA is expected to deeply survey the entire X-ray sky. The driving science is the detection of 100.000 distant galaxy clusters in order to study the large scale structure in the Universe and test cosmological models including Dark Energy. In addition, eROSITA will detect about 3 million Active Galaxies, widening our view on the evolution of supermassive black holes. eROSITA will also provide new clues on other astrophysical topics, like X-ray binaries and the diffuse galactic emission.