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The warm neutral medium produces most of the 21-cm line emission from hydrogen detected by radio telescopes, although atomic hydrogen in the cold neutral medium also contributes, both in emission and by absorption of photons from background warm gas ('H I self-absorption', HISA). While not important for cooling, the 21-cm line is easily ...
The following tables list molecules that have been detected in the interstellar medium or circumstellar matter, grouped by the number of component atoms.Neutral molecules and their molecular ions are listed in separate columns; if there is no entry in the molecule column, only the ionized form has been detected.
NGC 604, a giant H II region in the Triangulum Galaxy. An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. [1] It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic centimetre.
A year later, Lewis Snyder and his colleagues found interstellar formaldehyde. Also in the same year George Carruthers managed to identify molecular hydrogen. The numerous detections of molecules in interstellar space would help pave the way to the discovery of molecular clouds in 1970. [4]
They are detected primarily in the 21 cm line of neutral hydrogen, [6] and typically have a lower portion of heavy elements than is normal for interstellar clouds in the Milky Way. Theories intended to explain these unusual clouds include materials left over from the formation of the galaxy, or tidally-displaced matter drawn away from other ...
(H is the chemical symbol for hydrogen, and "I" is the Roman numeral. It is customary in astronomy to use the Roman numeral I for neutral atoms, II for singly-ionized—HII is H + in other sciences—III for doubly-ionized, e.g. OIII is O ++ , etc. [ 1 ] ) These regions do not emit detectable visible light (except in spectral lines from ...
The region of ionized hydrogen surrounding the massive stars is known as an H II region while the shells of neutral hydrogen surrounding the H II region are known as photodissociation region. Examples of star-forming regions are the Orion Nebula, the Rosette Nebula and the Omega Nebula. Feedback from star-formation, in the form of supernova ...
The term outward space existed in a poem from 1842 by the English poet Lady Emmeline Stuart-Wortley called "The Maiden of Moscow", [13] but in astronomy the term outer space found its application for the first time in 1845 by Alexander von Humboldt. [14] The term was eventually popularized through the writings of H. G. Wells after 1901. [15]