An Etymological Dictionary of Astronomy and Astrophysics

A relatively small, dense, and hot → molecular clump occurring in regions of → massive star formation. HMCs have diameters ≤ 0.1 pc, densities ≥ 10⁷ cm^-3, and temperatures ≥ 100 K.
The densest hot cores are traced in → ammonia (NH₃) and possess densities of 10⁸ cm^-3, sizes down to 0.05 pc and temperatures of up to 250 K. Hot molecular cores are generally associated with → compact H II regions and → ultracompact H II regions. High angular resolution observations suggest that HMCs are internally heated by embedded sources, since temperature and density increases toward the center as expected if star formation is occurring close to the core center. Same as → hot core.

See also: → hot; → molecular; → core.