| Astrophysics (Index) | About |
An emission nebula is a nebula that emits EMR, as opposed to an absorption nebula or reflection nebula. The term bright nebula refers to an emission or reflection nebula. Emission nebulae consist of gas heated until it is ionized and glows, invariably by one or more hot stars. The two common types of emission nebulae are HII regions and planetary nebulae, and a third, less frequent type is a visible supernova remnant. Red is the most common visible-light color, e.g., from Balmer emission lines. Emission nebulae tend to be associated with star-forming regions, due to such regions' young massive stars producing ionizing radiation, and because groups of planetary nebulae can result from a bunch of such stars formed together that are simultaneously reaching the end of their lives.