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A molecular cloud—sometimes called a stellar nursery if star formation is occurring within—is a type of interstellar cloud of which the density and size permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H 2), and the formation of H II regions.
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.
An HI region or H I region (read H one) is a cloud in the interstellar medium composed of neutral atomic hydrogen (HI), in addition to the local abundance of helium and other elements. (H is the chemical symbol for hydrogen, and "I" is the Roman numeral.
NGC 604, a giant H II region in the Triangulum Galaxy, taken by the Hubble Space Telescope. An H II 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 ...
About half the total mass of the Milky Way's galactic ISM is found in molecular clouds [9] and the galaxy includes an estimated 6,000 molecular clouds, each with more than 100,000 M ☉. [10] The nebula nearest to the Sun where massive stars are being formed is the Orion Nebula , 1,300 light-years (1.2 × 10 16 km) away. [ 11 ]
Interstellar clouds also provide a medium to study the presence and proportions of metals in space. The presence and ratios of these elements may help develop theories on the means of their production, especially when their proportions are inconsistent with those expected to arise from stars as a result of fusion and thereby suggest alternate ...
Observations and measurements of cosmic dust in different regions provide an important insight into the Universe's recycling processes; in the clouds of the diffuse interstellar medium, in molecular clouds, in the circumstellar dust of young stellar objects, and in planetary systems such as the Solar System, where astronomers consider dust as ...
The Local Bubble, or Local Cavity, [3] is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way.It contains the closest of celestial neighbours and among others, the Local Interstellar Cloud (which contains the Solar System), the neighbouring G-Cloud, the Ursa Major moving group (the closest stellar moving group) and the Hyades (the nearest open cluster).