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Welcome to the home page of

Friedrich (Fritz) Röpke.

I'm Professor of Theoretical Astrophysics at the Center for Astronomy of Ruprecht-Karls University Heidelberg, Germany. Large parts of my research activities are hosted by the Heidelberg Institute for Theoretical Studies, where I lead the Physics of Stellar Objects group.

Research Statement: Physics of Stellar Objects

Most places in the Universe are rather empty — at least when considering their material content. When matter condenses, however, things get interesting as stellar objects form. These are central to the work in my group Physics of Stellar Objects.

Why not simply “Stellar Astrophysics”?

There is nothing wrong with stellar astrophysics, really. It would describe the field I am interested in well, but it also evokes the notion of classical stellar evolution modeling which is connected to, but not in the focus of my work. My aim is to develop the theoretical and physical concepts to gain new insights into the mechanisms at work in stars with the long-term goal to improve stellar models.

“Stellar Objects” or “stars”?

Using the somewhat made-up term stellar objects instead of stars is intended to reflect my broader interest in astrophysical objects at the stellar scale: in addition to “normal stars” it also includes compact stellar objects — such as white dwarfs and neutron stars. This distinction also refers to the very different physical conditions that are found in stellar objects and the implied approaches to model them.

The “Physics of...” or “Computational stellar astrophysics”?

As macroscopic objects, effective theories such as thermodynamics and fluid dynamics are used to describe stars, but their conditions in the interiors can be so extreme that quantum mechanics, nuclear, and particle physics dominate the properties of matter. It is this broad variety of effects and their interplay that fascinates me and the term physics of... reflects the interest in the physical mechanisms at play in stars.
The involvement of various physical processes makes realistic stellar models so complex that analytic approaches quickly become insufficient for a detailed description. Many of the processes are three-dimensional in their nature and reducing the dimensionality of the models introduces coarse approximations. Moreover, reaching as much detail as possible is mandatory when aiming at verification of the models by comparison with astronomical data. Consequently, the sets of equations underlying the stellar models are solved numerically. For this, my group performs simulations on some of the world's leading supercomputers.
Although the numerical algorithms are rather involved and my group actively works on developing new techniques, these remain tools to reach my goal as a physicist: an improved understanding of the Physics of stellar objects.

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