Research Interests
Physics of the interstellar medium and star formation
The stars that we see in the night sky have not always been there, and will not remain forever. They are part of a cycle of matter in galaxies, which includes clouds of gas and dust between the stars, the so-called interstellar medium (ISM). At the end of their lives, stars return much of their mass to the ISM, from which then new generations of stars are born. How exactly this process works and what determines the numbers, masses, and other properties of stars and planets is a question that my research focuses on

Astrochemistry
The gas in interstellar clouds is mostly hydrogen, but also contains traces of other molecules. Some of these are commonly known on Earth, such as carbon monoxide (CO), ammonia (NH3), and methanol (CH3OH), while others only occur under special laboratory conditions, such as formyl (HCO+). Some species were even found in space before they were known on Earth! The chemical composition of interstellar gas clouds reveals a great deal about their physical properties, and at the same time tells us about basic chemical processes that are hard or impossible to study on Earth. My research focuses on two specific areas: the ionization rates of interstellar clouds, and their temperature history

Molecular spectroscopy and radiative transfer
Astronomers use a technique called spectroscopy to observe specific molecules in space, and interpreting these observations requires specialized computer programs. My group develops such tools, in particular the fast non-LTE solver RADEX for clouds with a simple slab geometry, and the sophisticated Monte Carlo program RATRAN for spherical and cylindrical objects such as protostellar envelopes and disks. The molecular input data for both programs are collected in a database called LAMDA

Exoplanets and astrobiology
Since 1995, thousands of planets have been discovered around nearby stars; probably there are more planets than stars in the Universe. About 1% of planets resemble the Earth in size, composition, and temperature, which makes them candidates for habitable worlds. My research focuses on the question which conditions are required (and optimal) for life to originate (or at least survive) on planets, and how we may recognize signs of such life.