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The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 7.62±0.32 kpc (~25,000±1,000 ly) from the Earth[1][2][3][4][5][6] in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest. It is believed that there is a supermassive black hole at the Galactic Center of the Milky Way.[7]

The Galactic Center as seen by one of the 2MASS infrared telescopes.

Contents

Proof of existence and location

Because of interstellar dust along the line of sight, the Galactic Center cannot be studied at visible, ultraviolet or soft X-ray wavelengths. The available information about the Galactic Center comes from observations at gamma ray, hard X-ray, infrared, sub-millimetre and radio wavelengths.

Coordinates of the Galactic Center were first found by Harlow Shapley in his 1918 study of the distribution of the globular clusters. In the Equatorial coordinate system they are: RA 17h45m40.04s, Dec -29° 00' 28.1" (J2000 epoch).

Supermassive black hole

The complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center, and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of our Galaxy. Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than the black hole. The latter is too small to see with present instruments.

A study in 2008 which linked radio telescopes in Hawaii, Arizona and California (Very Long Baseline Interferometry) measured the diameter of Sagittarius A* to be 0.3 AU (44 million kilometers).[8][9]

Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany using Chilean telescopes have confirmed the existence of a super massive black hole at the galactic center. This black hole is of the order 4 million solar masses.[10]

Stellar population

Galactic Center of Milky way and a meteor

The central parsec around Sagittarius A* contains thousands of stars. Although most of them are old red main sequence stars, the Galactic Center is also rich in massive stars. More than 100 OB and Wolf-Rayet stars have been identified there so far. They seem to have all been formed in a single star formation event a few million years ago. The existence of these relatively young (though evolved) stars was a surprise to experts, who expected the tidal forces from the central black-hole to prevent their formation. This paradox of youth is even more remarkable for stars that are on very tight orbits around Sagittarius A*, such as S2. The scenarios invoked to explain this formation involve either star formation in a massive star cluster offset from the Galactic Center that would have migrated to its current location once formed, or star formation within a massive, compact gas accretion disk around the central black-hole. It is interesting to note that most of these 100 young, massive stars seem to be concentrated within one (according to the UCLA group) or two (according to the MPE group) disks, rather than randomly distributed within the central parsec. This observation however does not allow definite conclusions to be drawn at this point.

Star formation does not seem to be occurring currently at the Galactic center, although the Circumnuclear Disk of molecular gas that orbits the Galactic center at two parsecs seems a fairly favorable site for star formation. Work presented in 2002 by Antony Stark and Chris Martin mapping the gas density in a 400 light year region around the galactic center has revealed an accumulating ring with a mass several million times that of the Sun and near the critical density for star formation. They predict that in approximately 200 million years there will be an episode of starburst in the galactic center, with many stars forming rapidly and undergoing supernovae at a hundred times the current rate. The starburst may also be accompanied by the formation of galactic jets as matter falls into the central black hole. It is thought that the Milky Way undergoes a starburst of this sort every 500 million years.

See also

References

  1. ^ Reid, Mark J. (1993). "The distance to the center of the Galaxy". Annual review of astronomy and astrophysics 31: 345–372. doi:10.1146/annurev.aa.31.090193.002021. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993ARA%26A..31..345R&amp. Retrieved 2007-05-10.  
  2. ^ Eisenhauer, F.; Schödel, R.; Genzel, R.; Ott, T.; Tecza, M.; Abuter, R.; Eckart, A.; Alexander, T. (2003). "A Geometric Determination of the Distance to the Galactic Center". The Astrophysical Journal 597: L121–L124. doi:10.1086/380188. http://adsabs.harvard.edu/abs/2003astro.ph..6220E. Retrieved 2007-05-10.  
  3. ^ Horrobin, M.; Eisenhauer, F.; Tecza, M.; Thatte, N.; Genzel, R.; Abuter, R.; Iserlohe, C.; Schreiber, J.; Schegerer, A.; Lutz, D.; Ott, T.; Schödel, R. (2004). "First results from SPIFFI. I: The Galactic Center" (PDF). Astronomische Nachrichten 325: 120–123. doi:10.1002/asna.200310181. http://www.mpe.mpg.de/SPIFFI/preprints/first_result_an1.pdf. Retrieved 2007-05-10.  
  4. ^ Eisenhauer, F. et al. (2005). "SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month". The Astrophysical Journal 628 (1): 246–259. doi:10.1086/430667. http://adsabs.harvard.edu/abs/2005ApJ...628..246E. Retrieved 2007-08-12.  
  5. ^ Majaess D. J., Turner D. G., Lane D. J. (2009). Characteristics of the Galaxy according to Cepheids, MNRAS
  6. ^ SINFONI in the Galactic Center: young stars and IR flares in the central light month. http://arxiv.org/abs/astro-ph/0502129.  
  7. ^ Schödel, R.; et al. (2002). "A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way". Nature 419 (6908): 694–696. doi:10.1038/nature01121.  
  8. ^ Doeleman, Sheperd S.; et al. (2008). "Event-horizon-scale structure in the supermassive black hole candidate at that Galactic Centre". Nature 455 (7209): 78–80. doi:10.1038/nature07245.  
  9. ^ Reynolds, Christopher S. (2008). "Bringing black holes into focus". Nature 455 (7209): 39. doi:10.1038/455039a.  
  10. ^ "Black hole confirmed in Milky Way". BBC. December 9, 2008. http://news.bbc.co.uk/1/hi/sci/tech/7774287.stm. Retrieved 2008-12-10.  

Further reading

  • Eckart, A.; Schödel, R.; Straubmeier, C. (2005). The Black Hole at the Center of the Milky Way. London: Imperial College Press. ISBN 1860945678.  
  • Melia, Fulvio (2003). The Black Hole in the Center of Our Galaxy. Princeton: Princeton University Press. ISBN 0691095051.  
  • Melia, Fulvio (2007). The Galactic Supermassive Black Hole. Princeton: Princeton University Press. ISBN 9780691131290.  

External links

Coordinates: Sky map 17h 45m 40.04s, −29° 00′ 28.1″

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