|giant molecular cloud|
|Observation data: J2000.0  epoch|
|Right ascension||17h 47m 20.4s |
|Declination||−28° 23′ 07″ |
|Designations||Sagittarius B2, Sgr B2|
Sagittarius B2 (Sgr B2) is a giant molecular cloud of gas and dust that is located about 120 parsecs (390 ly) 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 (150 ly) across. The total mass of Sgr B2 is about 3 million times the mass of the Sun. The mean hydrogen density within the cloud is 3000 atoms per cm3, which is about 20–40 times denser than a typical molecular cloud.
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 prolific star formation. The first 10 H II regions discovered were designated A through J. 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). 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.
Temperatures in the cloud vary from 300 K (27 °C) in dense star-forming regions to 40 K (−233.2 °C) in the surrounding envelope. Because the average temperature and pressure in Sgr B2 are low, chemistry based on the direct interaction of atoms is exceedingly 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.
The molecular components of this cloud can be readily observed in the 102–103 μm range of wavelengths. 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.
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 ago by the supermassive black hole (SMBH) at the galaxy's core, Sagittarius A*. The total luminosity from this outburst is an estimated million times stronger than the current output from Sagittarius A*. This conclusion has been supported in 2011 by Japanese astronomers who observed the galactic center with the Suzaku satellite.
- "NAME SGR B2 -- Molecular Cloud". SIMBAD. Retrieved 2014-03-14.
- Chown, Marcus (November 27, 1999). "Star attraction". New Scientist. Retrieved 2007-10-29.
- Solomon, P. M. (1978). Giancarlo Setti and Giovanni G. Fazio, ed. Physics of Molecular Clouds from Millimeter Wave Length Observations. Infrared Astronomy (New York: Springer). ISBN 90-277-0871-1.
- Goldsmith, Paul F.; Lis, Dariusz C.; Hills, Richard; Lasenby, Joan (1990). "High angular resolution submillimeter observations of Sagittarius B2". Astrophysical Journal 350: 186–194. Bibcode:1990ApJ...350..186G. doi:10.1086/168372.
- Lis, Dariusz C.; Goldsmith, Paul F. (1990). "Modeling of the continuum and molecular line emission from the Sagittarius B2 molecular cloud". Astrophysical Journal, Part 1 356: 195–210. Bibcode:1990ApJ...356..195L. doi:10.1086/168830.
- Takagi, Shin-ichiro; Murakami, Hiroshi; Koyama, Katsuji (2002). "X-Ray Sources and Star Formation Activity in the Sagittarius B2 Cloud Observed with Chandra". The Astrophysical Journal 573 (1): 275–282. arXiv:astro-ph/0203035. Bibcode:2002astro.ph..3035T. doi:10.1086/340499.
- Wolstencroft, Ramon D.; William Butler Burton (1988). Millimetre and Submillimetre Astronomy. Springer. ISBN 90-277-2763-5.
- de Vicente, P.; Martin-Pintado, J.; Wilson, T. L. (March 10–15, 1996). "A Hot Ring in the SGR B2 Molecular Cloud". Proceedings Astronomical Society of the Pacific Conference Series. La Serena, Chile: Astronomical Society of the Pacific. pp. 64–67. Retrieved 2007-10-29.
- S. E. Cummins, R. A. Linke, P. Thaddeus (1986). "A survey of the millimeter-wave spectrum of Sagittarius B2". Astrophysical Journal Supplement Series 60: 819–878. Bibcode:1986ApJS...60..819C. doi:10.1086/191102.
- Staff (January 28, 2005). "Integral rolls back history of Milky Way's super-massive black hole". Hubble News Desk. Retrieved 2007-10-31.
- M. G. Revnivtsev et al. (2004). "Hard X-ray view of the past activity of Sgr A* in a natural Compton mirror". Astronomy and Astrophysics 425: L49–L52. arXiv:astro-ph/0408190. Bibcode:2004A&A...425L..49R. doi:10.1051/0004-6361:200400064.
- M. Nobukawa et al. (2011). "New Evidence for High Activity of the Supermassive Black Hole in our Galaxy". The Astrophysical Journal Letters 739: L52. arXiv:1109.1950. Bibcode:2011ApJ...739L..52N. doi:10.1088/2041-8205/739/2/L52.
- R. M. Gaume et al. (October 31, 2007). "Sagittarius B2 (North)". National Radio Astronomy Observatory. Retrieved 2007-10-31.