Hello,
I am professor for theoretical astrophysics at Heidelberg University working at the Institute for Theoretical Astrophysics (ITA) at the Center for Astronomy (ZAH). My research activities focus on the formation of stars at present days and inthe early universe, on the dynamics of the interstellar medium, on astrophysical turbulence, and on the development of numerical methods for computational astrophysics.
For an overview of my curriculum vitae follow this LINK.
For my website at the Center for Astronomy at Heidelberg University follow this LINK.
In 2020, I received an ERC synergy grant together with Patrick Hennebelle (CEA, Saclay), Sergio Molinari (INAF, Rome), and Leonardo Testi (ESO, Garching). More information is found on this LINK.
Currently, I am member of the 2024/25 Class of Fellows at the Radcliffe Institute for Advanced Studies at Harvard University and guest at the Harvard-Smithsonian Center for Astrophysics during my sabbatical at Harvard University.
Current Research Highlight
February 2025: The radiative torque spin-up efficiency of ballistic dust-grain aggregates
Jäger, Jonathan A., Reissl, Stefan, Klessen, Ralf S.: Astronomy & Astrophysics, 692, A244, 1 – 15. [A&A link]
Fractal dust grain with effective radius of 250 nm. The rotation axis is depicted as the red arrow and is associated with the direction of the maximum moment of inertia.
It is quintessential for the analysis of the observed dust polarization signal to understand the rotational dynamics of interstellar dust grains. Additionally, high rotation velocities may rotationally disrupt the grains, which impacts the grain-size distribution. We aim to constrain the set of parameters for an accurate description of the rotational spin-up process of ballistic dust grain aggregates driven by radiative torques (RATs). We modeled the dust grains as complex fractal aggregates grown by the ballistic aggregation of uniform spherical particles (monomers) of different sizes. A broad variation of dust materials, shapes, and sizes were studied in the presence of different radiation sources. We find that the canonical parameterization for the torque efficiency overestimates the maximum angular velocity ωRAT caused by RATs acting on ballistic grain aggregates. To resolve this problem, we propose a new parameterization that predicts ωRAT more accurately. We find that RATs are most efficient for larger grains with a lower monomer density. This manifests itself as a size- and monomer-density dependence in the constant part of the parameterization. Following the constant part, the parameterization has two power laws with different slopes that retain universality for all grain sizes. The maximum grain rotation does not scale linearly with radiation strength because different drag mechanisms dominate, depending on the grain material and environment. The angular velocity ωRAT of individual single dust grains has a wide distribution and may even differ from the mean by up to two orders of magnitude. Even though ballistic aggregates have a lower RAT efficiency, strong sources of radiation (stronger than ≈100 times the typical interstellar radiation field) may still produce rotation velocities high enough to cause the rotational disruption of dust grains.
Earlier Research Highlights
For the all monthly research highlights follow this LINK.
Funding Sources
