Cold Interstellar Molecular Clouds as Cosmic Ray Detectors

Barnard 68

A composite visible and near-infrared image of the interstellar dark cloud, Barnard 68. The gas and dust in its interior is very cold, but can be heated by cosmic rays. A new study predicts that the infrared emission lines of molecular hydrogen in dark clouds provide key diagnostics of cosmic rays in the interstellar medium. Credit: ESO; VLT/ANTU and FORS1

The ionization of the neutral gas in an interstellar molecular cloud plays a key role in the cloud’s evolution, helping to regulate the heating and cooling processes, the chemistry and molecule formation, and coupling the gas to magnetic fields.

Usually starlight provides this ultraviolet radiation, but it is mostly restricted to localized regions near massive stars. For the bulk of the neutral gas in the DOI: 10.1038/s42005-020-0293-7