Molecular Clouds and Star Formation
Molecular Cloud Formation
Molecular clouds form by the condensation of cold and dense gas out of the warm, diffuse, and magnetised interstellar medium (ISM). This condensation is the result of thermal and dynamical instabilities, which arise due to processes on larger scales, such as gravitational instabilities or collisions of supernova remnant shells. On smaller scales, also turbulence is major ingredient in controlling the formation of dense structures. In this research project we analyse the formation of molecular clouds by turbulent and magnetised colliding flows and the subsequent star formation process.
In the pictures above one can see the formation of a turbulent molecular cloud in the edge-on plane (top) and the face-on plane (bottom). The internal structure of the cloud is filamentary and the filaments and clumps are embedded in a diffuse, warm medium. Since the ISM is subject to heating and cooling processes, these substructures are in pressure equilibrium with the diffuse phase and are thus longlived entities, which eventually collapse to form a star (denoted by the black dots).
Molecular Cloud Formation With Varying Initial Conditions
The above mentioned study assumes a perfect alignment of the colliding flows with the background magnetic field. But this scenario is an idealised one, since turbulence, galactic accretion and stellar feedback drive turbulence on a wide range of scales. Due to the interaction of the turbulent velocity field with the magnetic field, the latter will have a strong non-uniform component. Thus, large scale motions are able to move at an certain angle with respect to the local background magnetic field. If this is the case, the question arises whether molecular clouds are still able to build up and whether star formation is still the outcome. Our research group aims at understanding the outcome of such non-idealised initial conditions by studying this process with varying inclinations of the flow with respect to the background magnetic field and varying magnetic field strengths. The picture shows the column density as function of spatial coordinates (in pc) for an initial inclination of one flow of 60 degrees. The blue lines denote magnetic field lines and the black dot represents a sink particle. Click on the image to see a movie of this simulation.
Feedback in Molecular Clouds
Molecular clouds form stars with a broad mass spectrum, which tends to be bottom heavy (i.e. the distribution peaks at low masses) with a power-law tail at high masses. This distribution indicates that massive stars are rare. But despite their low occurrence, these massive stars are the most efficient agents in terms of stellar feedback. Since they are massive enough, they impact onto their parental cloud by means of ionising radiation, fast stellar winds and, finally, by supernovae feedback. During a supernovae, a huge amount of energy is released and injected into the ambient medium in a short amount of time, which is comparable to the overall energy input by the stellar wind. Due to this fact, supernova explosions are thought to disintegrate entire molecular clouds and thus stop the collapse of the cloud and its subsequent star formation process. On the other hand the feedback by massive stars can drive turbulence on molecular cloud scales. In this project we determine the influence of supernova feedback by massive stars on their parental molecular cloud. In detail we analyse the resulting cloud morphology and dynamics and study the impact on the formation of stars within the densest regions.