Sagittarius B2 (Sgr B2) is a giant molecular cloud of gas and dust that is located about 120 parsecs from the center of the Milky Way. This complex is the largest molecular cloud in the vicinity of the core and one of the largest in the galaxy, spanning a region about 45 parsecs across.^[1] The total mass of Sgr B2 is about 3 million times the mass of the Sun.^[2] The mean hydrogen density within the cloud is 3000 atoms per cm³, which is about 20–40 times more dense than a typical molecular cloud.^[3] A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... For other uses, see Milky Way (disambiguation). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

The internal structure of this cloud is complex, with varying densities and temperatures. The cloud is divided into three main cores, designated north (N), middle or main (M) and south (S) respectively. Thus Sgr B2(N) represents the north core. The sites Sgr B2(M) and Sgr B2(N) are sites of massive star formation. The first 10 H II regions discovered were designated A through J.^[4] H II regions A-G, I and J lie within Sgr B2(M), while region K is in Sgr B2(N) and region H is in Sgr B2(S).^[5] The 5-parsec-wide core of the cloud is a star-forming region that is emitting about 10 million times the luminosity of the Sun.^[6] NGC 604, a giant H II region in the Triangulum Galaxy. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ...

Temperatures in the cloud vary from 300 K in dense star-forming regions to 40 K in the surrounding envelope.^[7] Because the average temperature and pressure in Sgr B2 are low, chemistry based on the direct interaction of atoms is excedingly slow. However, the Sgr B2 complex contains cold dust grains consisting of a silicon core surrounded by a mantle of water ice and various carbon compounds. The surfaces of these grains allow chemical reactions to occur by accreting molecules that can then interact with neighboring compounds. The resulting compounds can then evaporate from the surface and join the molecular cloud.^[1]

The molecular components of this cloud can be readily observed in the 10²–10³ m range of wavelengths.^[1] About half of all the known interstellar molecules were first found near Sgr B2, and nearly every other currently known molecule has since been detected in this feature.^[8] This is a list of molecules that have been detected in the interstellar medium, grouped by the number of component atoms. ...

The European Space Agency's gamma-ray observatory INTEGRAL has observed gamma rays interacting with Sgr B2, causing x-ray emission from the molecular cloud. This energy was emitted about 350 years before by the supermassive black hole (SMBH) at the galaxy's core. The total energy from this outburst is an estimated million times stronger than the current output from the SMBH.^[9] “ESA” redirects here. ... For the music band, see Gamma Ray (band). ... This article is about the concept of integrals in calculus. ...

See also

• List of molecules in interstellar space

This is a list of molecules that have been detected in the interstellar medium, grouped by the number of component atoms. ...

References

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External links

• R. M. Gaume et al (October 31, 2007). Sagittarius B2 (North). National Radio Astronomy Observatory. Retrieved on 2007-10-31.