Institut für Astronomie & Astrophysik


Theory of Accretion Discs

Bertram Bitsch, Philipp Buchegger, Markus Flaig, Willy Kley, Stefan Kolb, Farzana Meru, Tobias Müller

Hubble view of the Orion nebula showing five young
stars of which four are surrounded by protoplanetary discs (Courtesy: NASA)

Our research focusses on the physical structure and dynamics of accretion discs. Examples include circumstellar discs around T-Tauri stars, consisting mainly of gas and also a small amount of interstellar dust. In accretion discs the gas rotates with nearly Keplerian velocity around the host star, spirals slowly inwards and is accreted onto the central star. In our group we study various aspects of accretion disc physics.

Planet Formation

Bertram Bitsch, Simeon Carstens, Ralf Geretshauser, Willy Kley, Farzana Meru, Tobias Müller, Alexander Seizinger

Simulated image of a self-gravitating disc undergoing fragmentation

Planet formation has been an area which has been studied in great detail with respect to the Solar System. The discovery of hundreds of extra-solar planets since the mid-1990s has put the field into a much larger context. A revision of the major aspects of classical planet formation theory is required. In our group we study various aspects of planet formation within the sequential accretion and gravitational instability scenario.

Astrophysical Jets

Matthias Stute

Hubble view of the Protostellar Jet HH 47
(Courtesy: NASA)

Astrophysical jets are ubiquitous, occurring in a variety of objects on very different size and mass scales. They can be produced by pre-main sequence stars in young stellar objects, by post-AGB stars in pre-planetary and planetary nebulae, by white dwarfs in supersoft X-ray sources and symbiotic stars, by neutron stars in X-ray binaries, by stellar black holes in black hole X-ray binaries and by supermassive black holes in the case of active galactic nuclei. However, there are still many open questions.

We investigate jets with analytical models, numerical simulations and observations with several space telescopes.

Individual Projects

Thermal creep in lightmills

Willy Kley, Daniela Skoropad, David Wharam (PIT)

A lightmill (Courtesy: Wikipedia)

In the so-called MEMS (micro-electro-mechanical-systems) we see effects that also occur in rarefied gases. To get a better understanding of these effects, we examine the behaviour of lightmills. A lightmill consists of four vanes, which have a shiny and a blackened side. Under illumination, the blackended side heats up and the mill starts to rotate in the direction of shiny sides. This rotation only occurs in a small pressure regime, typically at pressures of around 1 Pa. At such low presures collisions between particles are scarce and therefore several boundary effects have to be taken into account:

Numerical results are compared with experiments at PIT.