Molecular Clouds (a review)

TL;DR

This review summarizes advances in understanding molecular cloud formation, structure, and star formation, highlighting the role of spiral arms, inhomogeneities, and the potential link between core mass and star mass.

Contribution

It synthesizes recent progress in molecular cloud research, emphasizing the origin of cloud structures and their relation to star formation processes.

Findings

Molecular clouds form from compressed HI in spiral arms.

Cloud structure results from magnified HI inhomogeneities.

Core mass may determine star mass more than formation details.

Abstract

We review the progress made in understanding molecular cloud formation and evolution toward star formation since the first Crete conference in 1990. It now seems clear that molecular clouds in the Galaxy at least form from compressed HI entering a spiral arm. The internal clumpy structure within clouds probably results from the magnification of inhomogeneities in the precursor HI. This structure is self-similar in nature independent of the star forming nature of the cloud. However, at high densities and small scales, there are departures from self-similarity that may be related to the mass scale of stars. If confirmed, it may be that the mass of a star is related more to the mass of the core from which it forms than by the details of the formation process itself.