High-Energy astrophysics deals with phenomena which occur at the end of the stellar lifetime, like supernova explosions, neutron stars, and stellar black holes. Far outside our own Galaxy, the X-ray and Gamma-ray sky is dominated by active galaxies (radio galaxies, Seyfert galaxies, and quasars) with accreting supermassive black holes in their centers and by clusters of galaxies, the largest physical formations of our universe. Also, normal stars and galaxies can be studied with modern X-ray telescopes. And even comets and planets in the solar system are seen in X-rays. The research activities of the high-energy group cover all these high-energetic phenomena.
In the past decade, studies of the local Universe have established the presence of supermassive black holes (SMBH) in the nuclei of virtually all galaxies with a bulge/spheroidal component, dramatically changing our perception of this class of objects, and implying a clear relationship between the growth of SMBH and that of the galaxy. Because the cosmological growth of SMBHs is mostly due to accretion of matter during active phases and the energy released in the process of accretion can be higher than the total binding energy of a massive galaxy, active galactic nuclei (AGN) can in principle have a profound effect on the galaxy formation and evolution processes. X-ray emission offers a unique signpost of accretion of matter onto the supermassive black holes in AGN, being able to penetrate through obscuring material and overcome light from stellar processes. Investigating whether and how nuclear black holes influence their host galaxies, and vice versa, has been and remains to be a major focus in the activity of the MPE HE Group.
Clusters and groups of galaxies are the largest objects in the universe which are bound together by gravitational attraction. When viewed in the optical waveband, they consist of 10s to 1000s of galaxies. However, most of the mass in a cluster is in the form of unseen dark matter, which can only be studied indirectly. The galaxies make up only a small fraction of the normal, light-emitting matter in a cluster. Most of that matter is in the form of a hot plasma at 10s of millions of degrees, that emits brightly by its X-ray emission. Therefore X-ray observations of clusters are vital in finding them and studying their nature. In the MPE HE Group we are engaged in making surveys of galaxy clusters, as their distribution tells us a great deal about the evolution of the universe. In addition, we also study clusters themselves, as they are fascinating massive laboratories where we can study the physics of dark matter, black holes, hot plasmas, accelerated particles and cold gas.
The most compact and extreme objects in the Universe, e.g., black holes and neutron stars, give rise to some of the most violent and energetic phenomena known to mankind. Research in the High-Energy Group of the MPE specifically focusses on a few key aspects, such as accretion, strong gravity, and gamma-ray bursts.
The interstellar medium with its structure and dynamics plays a key role in galactic evolution, being the birthplace of stars. At MPE star formation and its interstellar conditions and signatures are studied by our colleagues in the infrared group, while the high-energy group studies the terminal stages of stellar evolution and their impacts on the hot, dynamic, and relativistic phases of the interstellar medium. Stellar outputs, their wind and explosion energies and their ejecta lead to bubbles and superbubbles up to 1 kpc in size, they thus shape the state and dynamics of interstellar gas. Magnetic field configurations follow from this and determine observable radiation such as, e.g., synchrotron emission. High energy astronomy provides more observational tools through emission from relativistic particles in the ISM, and from interstellar radioactivities, in addition to the thermal emission which still can be traced up to X-ray energies. Lessons from specific emission processes, and from source regions and its objects, are transferred to populations of sources or entire galaxies. This connects these nearby universe studies to surveys of the more distant universe and to models of stellar and galaxy evolution.
Two main projects drive presently the detector development of the high-energy group of MPE: the PNCCD detectors for the eROSITA project and the DEPFET active pixel detectors for the WFI instrument of ATHENA. While the eROSITA has reached its final phase of development, ATHENA has recently started. Two different detectors concepts have been chosen to fulfil the diverse specifications of the projects optimally. However, both detector developments have in common their application for spectroscopy and imaging of X-ray photons on a space telescope with high time resolution and excellent quantum efficiency.