ASTROPHYSICS

Interstellar turbulence shapes the structure of the multi-phase interstellar medium (ISM) and is a key process in the formation of molecular clouds as well as the build-up of star clusters in their interior. The key ingredient for our theoretical understanding of ISM dynamics and stellar birth is the sonic scale in the turbulent cascade, which marks the transition from supersonic to subsonic turbulence and produces a break in the turbulence power spectrum. To measure this scale and study the sonic transition region in detail, scientists, for the first time, ran a simulation with the unprecedented resolution of 10,048³ grid cells.

Understanding turbulence is critical for a wide range of terrestrial and astrophysical applications. For example, turbulence on earth is responsible for the transport of pollutants in the atmosphere and determines the movement of weather patterns. But turbulence plays a central role in astrophysics as well. For instance, the turbulent motions of gas and dust particles in protostellar disks enables the formation of planets. Moreover, virtually all modern theories of star formation rest on the statistics of turbulence (Padoan et al., 2014). Especially the theoretical assumptions about turbulence behind star formation theories allow the prediction of star formation rates in the Milky Way and in distant galaxies (Federrath & Klessen, 2012). Interstellar turbulence shapes the structure of molecular clouds and is a key process in the formation of filaments which are the building blocks of star-forming clouds. The key ingredient for all these models is the so-called sonic scale. The sonic scale marks the transition from supersonic to subsonic turbulence and produces a break in the turbulence power spectrum from E ∝ k⁻² to E ∝ k^−5/3 . While the power-law slopes of -2 and -5/3 for the supersonic and subsonic parts of the spectrum have been measured independently, there is no simulation currently capable of bridging the gap between both regimes. This is because previous simulations did not have enough resolution to separate the injection scale, the sonic scale and the dissipation scale.

The aim of this project is to run the first simulation that is sufficiently resolved to measure the exact position of the sonic scale and the transition region from supersonic to subsonic turbulence. A simulation with the unprecedented resolution of 10,000³ grid cells will be needed for resolving the transition scale.