What does a high density of around 5 x 10^9 m-3 indicate in a diffuse molecular cloud?

A density of around 5 x 10^9 m^-3 in a diffuse molecular cloud indicates a relatively high density environment compared to the surrounding interstellar medium. This level of density suggests that the cloud is dense and cold, creating favorable conditions for the process of star formation. In such environments, the molecules can collide and coalesce, leading to the gravitational instability needed for star formation.

Diffuse molecular clouds provide the necessary material and conditions where hydrogen molecules and other compounds can cluster together. The cold temperatures within these clouds, combined with high densities, allow for effective cooling and support the formation of denser clumps which may eventually form stars.

Higher densities would not typically indicate a highly ionized state or conditions suitable for supernovae, rather, they reflect the conditions necessary for gravitational collapse and star formation. Similarly, the density mentioned rules out the possibility of it being a low-density region or one where only large stars can form; star formation can occur across a range of stellar masses in high-density environments.