Star Formation and Interstellar Chemistry How do stars form out of these clouds of cold, molecular gas?

Why do molecules form and persist in these clouds Why do molecules form and persist in these clouds? Why don’t we see them elsewhere, like HII regions?

Gas Clouds and Gravitational Contraction Does a condensation in a cloud expand and disperse, or contract under its own gravity?

The Evolution of a Compression in a Cloud of Gas A competition between expansion (gas pressure) and contraction (gravity) Gas pressure determined by gas density and temperature Gravity determined by density and size of object “Jeans Length”

The Jeans Length For a given gas density and temperature, there is a size (of the compression) for which gravity wins

Within molecular clouds, clumps form which are dominated by gravity, and contract to form Protostars