http://arxiv.org/abs/1712.01160
Condensation of H2 in the ISM has long been seen as a possibility, either by deposition on dust grains or thanks to a phase transition combined with self-gravity. H2 condensation might explain the observed low efficiency of star formation and help hiding baryons in spiral galaxies.
Our aim is to quantify the solid fraction of H2 in the ISM due to a phase transition including self-gravity for different densities and temperatures, in order to use the results in more complex simulations of the ISM as subgrid physics.
We use molecular dynamics simulations of fluids at different temperatures and densities to study the formation of solids. Once the simulations reach a steady state, we calculate the solid mass fraction, energy increase and timescales. By determining the power laws measured over several orders of magnitude, we extrapolate to lower densities the higher density fluids that can be simulated with current computers.
The solid fraction and energy increase of fluids in a phase transition are above 0.1 and do not follow a power law. Fluids out of a phase transition are still forming a small amount of solids due to chance encounters of molecules. The solid mass fraction and energy increase of these fluids are linearly dependent on density and can easily be extrapolated. The timescale is below one second, the condensation can be considered as instantaneous.
The presence of solid H2 grains has important dynamic implications on the ISM, as they may be the building blocks for larger solid bodies when gravity in included. We provide the solid mass fraction, energy increase and timescales for high density fluids and extrapolation laws for lower densities.
A. Fuglistaler and D. Pfenniger
Tue, 5 Dec 17
17/96
Comments: Submitted to A&A