For 10 points, name these cold, dense interstellar clouds that are opaque due to their internal dust grains, examples of which include the Coalsack nebula.
Carbon located with the outer layers of these regions exists in an ionized form while their inner layers contain carbon monoxide, which primarily causes the cooling of these regions. Bernard cataloged 182 of these objects that were subsequently named after him and most T (*) Tauri variable stars are found within these regions. For 10 points, name these cold, dense interstellar clouds that are opaque due to their internal dust grains, examples of which include the Coalsack nebula.
Carbon located with the outer layers of these regions exists in an ionized form while their inner layers contain carbon monoxide, which primarily causes the cooling of these regions.
{dark} nebula (prompt on {nebula})