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The not-so-empty spaces between the stars –

New Priority Program investigates the interstellar medium

Munich, 06/18/2010

When we consider what lies beyond our planet, we tend to think of “outer space”. But the space between the stars is not empty. Interstellar space is filled with charged particles, neutral atoms, molecules and dust, and these constituents are exposed to the effects of stellar radiation in all its various forms, as well as to magnetic and gravitational forces. This mix of matter and forces makes up the interstellar medium (ISM). Understanding what happens in the ISM is crucial for solving the problem of how galaxies formed and evolve. After all, by definition, the stars they contain condense out of the ISM. The ISM is home to the gas, dust grains and organic molecules that supply the building blocks of stars, planets and living organisms. However, our knowledge of the structure and evolution of the ISM is still very patchy. A new 6-year Priority Program devoted to “Physics of the Interstellar Medium“, which will be financed by the Deutsche Forschungsgemeinschaft (DFG), intends to change that. The program, which will have a total budget of 14.4 million Euros, gets underway with a first call for research proposals in the Fall of 2010 and will be coordinated by the Physics Department at LMU Munich. The goal of the project is to cast new light on areas of the ISM that have managed to keep their workings hidden from us up to now. “We want to construct the first consistent physical model of the ISM, incorporating all the known and yet unknown highly complex dynamical and chemical processes that take place there. Such an integrated model would provide a solid physical basis for understanding unsolved problems in many areas of astrophysics in which the ISM plays a fundamental role”, says Andreas Burkert, Professor of Astronomy and Astrophysics at LMU and coordinator of the Priority Program.

The program will bring university-based groups together with researchers at several Max Planck Institutes as well as at the European Southern Observatory (ESO) to assemble the elements of a comprehensive and well-founded physical picture of the ISM and the dynamical processes that characterize it.  The ISM may not be empty, but by terrestrial standards it is pretty tenuous. Its average density is equivalent to one hydrogen atom per cubic cm, which is more rarefied than any vacuum attainable on Earth. It therefore provides an ideal environment for studies of the behavior of highly dilute gases, chemical processes, and atomic, molecular and solid-state physics, under conditions that are found nowhere else. Heavy elements make up fewer than 1% of the material present in interstellar gas, far less than the proportion found in stars. The vast majority (90%) of the matter in the ISM consists of atomic and molecular hydrogen, while helium accounts for a further 9%. In addition to the gas, the ISM contains dust grains, whose composition is not entirely clear. Silicates, graphite and iron have so far been identified. The grains are needle-shaped and orient themselves in the magnetic field of the Milky Way. Interstellar dust also obscures background stars by absorbing visible light, reradiating the energy in the infrared region of the spectrum.

The physics of the ISM plays a crucial role in many areas of astronomy. The origin and evolution of galaxies, the formation of stars, the amount, distribution and structure of the dust grains that contribute to the make-up of planets -- all of these processes are affected by the characteristics of the ISM. Despite its eminent importance for astrophysics, the structure and evolution of the ISM is still poorly understood. However, recent observations with high-performance telescopes herald a paradigm change in our perception of the ISM. It has become clear that the equilibrium models that have so far dominated our concepts of the ISM will have to be replaced. Highly dynamic models are needed that can adequately describe mixed, strongly coupled, interacting and turbulent gas flows, which are far from equilibrium and are constantly being buffeted by energetic shock fronts and radiation in ways that we do not yet understand. The research teams involved in the new program hope that, with the help of the resources being provided by the DFG, they can significantly accelerate the paradigm change. (ms)

 

Contact:
Prof. Dr. Andreas Burkert
Department für Physik
Lehrstuhl für Astronomie und Astrophysik
Phone: +49 (0) 89 / 2180 - 5992
E-mail: burkert@usm.uni-muenchen.de

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