CoachA molecular cloud is a region of the interstellar medium dense and opaque enough for its hydrogen to be mostly in molecules, , shielded by dust from the ultraviolet light of the stars that would break them; its temperature is about to . A dense core is a compact condensation inside a molecular cloud, a few tenths of a parsec across or less, with densities of to particles per cubic centimetre, from which a single star or a small group of stars forms.
| dark clouds | clumps | dense cores | |
|---|---|---|---|
| mass (solar masses) | – | 50–500 | 0.5–5 |
| size (pc) | 2–15 | 0.3–3 | 0.03–0.2 |
| mean density () | 50–500 | – | – |
| gas temperature (K) | about 10 | 10–20 | 8–12 |
| examples | Taurus, Musca | — | L1544, B68 |
