GCOE Member

Member Introductions



Education/Job Career History

  • 2005 - MSc (grade "with honors"), Faculty of Physics and Astronomy, Ruprecht-Karls-University Heidelberg, Germany
  • 2007 - JSPS pre-postdoctoral fellowship (short-term), Yukawa Institute for Theoretical Physics, Kyoto University, Japan
  • 2008 - PhD (grade "very good"), Faculty of Physics and Astronomy, Ruprecht-Karls-University Heidelberg, Germany
  • since 2008 - GCOE postdoctoral fellow, Department of Astronomy, Kyoto University, Japan

Research History

I started my research career as PhD student in the field of black hole accretion disks. My main interest therein was the question whether there exists an upper limit on the accretion rate and luminosity, in analogy to the classical Eddington limit of a star. The main difference to the stellar case is the non-spherical geometry of the accretion disk surrounding the black hole. Using analytical, semi-analytical and numerical methods, I studied these geometrical effects and other complications in the case of stellar mass black hole accretion disks. I analyzed 2D radiation-hydrodynamic simulation data with a radiative transfer code with special focus on the iron emission and absorption lines. The main results of this work are that the accretion rate can exceed the classical Eddington rate significantly, while the luminosity stays close to the classical Eddington luminosity, although it varies by one order of magnitude, depending of the orientation of the disk relative to the observer.

In a second project, I focused on the origin of viscosity in astrophysical disks, which is known to exceed terrestrial molecular viscosities by orders of magnitude. I investigated the contribution of convective turbulence, driven by viscous heating in accretion disks, to the total viscosity of the disk. The main conclusions here are that convective viscosity itself cannot account for the total viscosity, but it can add significantly to it. Yet, it requires a driving force which preserves the vertical temperature gradient and which could be provided by differential rotation, magneto-rotational instability or other processes.

Research Plan at GCOE

I started my postdoctoral position at the GCOE with the plan to touch new grounds: the chemical and physical evolution of protoplanetary disks. This is an extremely interesting and interdisciplinary topic in the relatively new field of research of astrobiology. In this work, I am interested in the temporal changes of the chemical composition of protoplanetary disks, i.e., disks in the intermediate phase between a collapsing molecular cloud and a young planetary system. Observational capabilities are now at the edge of providing detailed spectra of molecular emission and absorption lines of these protoplanetary disks, revealing an active organic chemistry in the inner 20AU of the disk. This is the region were future planet formation is believed to take place. It is therefore essential to understand and model the chemical evolution of these disks, especially the effects of accretion motion (i.e., a net inward transport of material from the outer, cool disk) and turbulent mixing or disk winds on the chemical evolution. One of the many questions of interest that I want to answer in this project is how much influence these processes have on the so-called snow-line of the system, i.e., the radial distance from the star until which water can exist in liquid form and which constrains the so-called habitable zone.


The research possibilities in Japan are great and the efforts of the GCOE leaders to open the program to foreigners remarkable. I can only encourage you to apply for a grant (GCOE, JSPS, ...) or a regular position to work in Japan for some years. Apart from a professional work environment, you will have a great time here enjoying Japanese culture, mountains, karaoke, food, ...