HII region

1. A cloudlike region in space where the interstellar medium consists of ionized rather than neutral hydrogen. HII regions are centered around stars with very high surface temperatures and brilliant luminosities, whose radiant energy is sufficient to heat the interstellar medium to the point that hydrogen is ionized. The most conspicuous and best-known HII region is the Orion Nebula.

Example Sentences

The Green Bank Telescope HII Region Discovery Survey, the first results of which were presented here on Wednesday at the 221st meeting of the American Astronomical Society, will provide astronomers with a detailed map of the spiral structure of the Milky Way.

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