Star Formation and its Impact on the ISM
Star formation occurs due to the collapse of dense parts of molecular clouds. To study star formation in detail it is important to also study the interstellar medium (ISM) and molecular clouds as precursors to the star formation. Once a star has formed it has a strong impact on the evolution of the surrounding medium. The UV radiation ionises the surrounding gas and creates a hot HII region. The heated gas starts to expand into the surrounding cold molecular cloud, creating a shock-wave. This shock-wave compresses the cold gas leading to pillar like structures. In the tip of those structures the formation of new stars is possible. Another important task to understand star formation in more detail is to study this process under extreme conditions. One example is the region close to the milky-way galactic centre black hole. Here tidal forces, which would disrupt a typical molecular cloud due to the deep potential, prevent star formation in the standard way. Still there are observations of a disk of stars on a sub-parsec scale near the black hole. The large scale impact of star formation on the ISM is due to supernovas. This process can heat and stir the ISM, leading to its multiphasic structure. It also enriches the ISM with elements of higher order. The so called local bubble, a region of low density gas inside which our solar system currently resides, is a interesting source to study the effect of supernova feedback. The bubble is believed to have formed by supernovas blowing out a large, peanut shaped region in the ISM. At the edges of this region, clusters of stars can form. The supernova feedback of those stars is directed towards the low density bubble (the so called champagne-effect) and enriches the bubble with heavy elements.