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Coordinates: Sky map 13h 26m 45.89s, −47° 28′ 36.7″
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The English astronomer [[John Herschel|John William Herschel]] recognized it first as a globular cluster in the 1830s.<ref>[http://www.spacetelescope.org/news/html/heic0809.html Black Hole found in enigmatic Omega Centauri]</ref> It orbits our [[galaxy]], the [[Milky Way]]. One of the few that can be seen with the naked eye, it is both the brightest and the largest known globular cluster associated with the Milky Way. Omega Centauri is located about 15,800 light-years (4,850 [[Parsec|pc]]) from Earth and contains several million [[Population II]] stars. The stars in its center are so crowded that they are believed to be only 0.1 light years away from each other. It is about 12 billion years old.
The English astronomer [[John Herschel|John William Herschel]] recognized it first as a globular cluster in the 1830s.<ref>[http://www.spacetelescope.org/news/html/heic0809.html Black Hole found in enigmatic Omega Centauri]</ref> It orbits our [[galaxy]], the [[Milky Way]]. One of the few that can be seen with the naked eye, it is both the brightest and the largest known globular cluster associated with the Milky Way. Omega Centauri is located about 15,800 light-years (4,850 [[Parsec|pc]]) from Earth and contains several million [[Population II]] stars. The stars in its center are so crowded that they are believed to be only 0.1 light years away from each other. It is about 12 billion years old.


Though it is not a star, Omega Centauri was given a [[Bayer designation]]. Unlike other globular clusters, it contains several generations of stars. It has been speculated that Omega Centauri may be the core of a [[dwarf galaxy]] several hundred times its present size, which was ripped apart and absorbed by our [[Milky Way]] [[galaxy]]. Omega Centauri's chemistry and motion in the galaxy is also consistent with this picture.
Though it is not a star, Omega Centauri was given a [[Bayer designation]]. Unlike other globular clusters, it contains several generations of stars. It has been speculated that Omega Centauri may be the core of a [[dwarf galaxy]] several hundred times its present size, which was ripped apart and absorbed by our [[Milky Way]] [[galaxy]]. Omega Centauri's chemistry and motion in the galaxy is also consistent with this picture. [[Kapteyn's star]] which is currently only 13 light years away is thought to originate from Omega Centauri.<ref>http://www.newscientist.com/article/mg20427334.100-backward-star-aint-from-round-here.html</ref>


Reporting in the [[April 1]], [[2008]] issue of The Astrophysical Journal, astronomers claimed to have found evidence of a [[intermediate-mass black hole]] at the center of Omega Centauri. The observations were made with NASA's [[Hubble Space Telescope]] and [[Gemini Observatory]] on Cerro Pachon in Chile.<ref>http://www.spacetelescope.org/news/html/heic0809.html</ref> Hubble's Advanced Camera for Surveys showed how the stars are bunching up near the center of Omega Centauri, as seen in the gradual increase in starlight near the center. Measuring the speed of the stars swirling near the cluster's center with the Gemini Observatory, the astronomers found that the stars closer to the core are moving faster than the stars farther away. The measurement implies that some unseen matter at the core is tugging on stars near it. By comparing these results with standard models, the astronomers determined that the most likely cause is the gravitational pull of a massive, dense object. They also used models to calculate the black hole's mass.<ref>[http://newswise.com/articles/view/539256/ Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri] Newswise, Retrieved on June 24, 2008.</ref>
Reporting in the [[April 1]], [[2008]] issue of The Astrophysical Journal, astronomers claimed to have found evidence of a [[intermediate-mass black hole]] at the center of Omega Centauri. The observations were made with NASA's [[Hubble Space Telescope]] and [[Gemini Observatory]] on Cerro Pachon in Chile.<ref>http://www.spacetelescope.org/news/html/heic0809.html</ref> Hubble's Advanced Camera for Surveys showed how the stars are bunching up near the center of Omega Centauri, as seen in the gradual increase in starlight near the center. Measuring the speed of the stars swirling near the cluster's center with the Gemini Observatory, the astronomers found that the stars closer to the core are moving faster than the stars farther away. The measurement implies that some unseen matter at the core is tugging on stars near it. By comparing these results with standard models, the astronomers determined that the most likely cause is the gravitational pull of a massive, dense object. They also used models to calculate the black hole's mass.<ref>[http://newswise.com/articles/view/539256/ Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri] Newswise, Retrieved on June 24, 2008.</ref>

Revision as of 20:17, 4 November 2009

ω Centauri
The globular cluster Omega Centauri. Credit ESO
Observation data (J2000 epoch)
ClassGlobular Cluster
ConstellationCentaurus
Right ascension13h 26m 45.89s[1]
Declination−47° 28′ 36.7″[1]
Distance15.8 ± 1.1 kly[2] (4.85 ± 0.35 kpc)
Apparent magnitude (V)3.7[3]
Apparent dimensions (V)36′.3[citation needed]
Physical characteristics
Mass~5 000 000[4] M☉ (~1•1037 kg)
Radius86 ± 6 ly[5]
Estimated age~12 Gyr[6]
Other designationsNGC 5139,[1] GCl 24,[1] ω Centauri[2]
See also: Globular cluster, List of globular clusters


Omega Centauri or NGC 5139 is a globular cluster[7] seen in the constellation of Centaurus, discovered by Edmond Halley in 1677 who listed it as a Nebula. Omega Centauri had been listed in Ptolemy's catalog 2000 years ago as a star. Lacaille included it in his catalog as number I.5. The English astronomer John William Herschel recognized it first as a globular cluster in the 1830s.[8] It orbits our galaxy, the Milky Way. One of the few that can be seen with the naked eye, it is both the brightest and the largest known globular cluster associated with the Milky Way. Omega Centauri is located about 15,800 light-years (4,850 pc) from Earth and contains several million Population II stars. The stars in its center are so crowded that they are believed to be only 0.1 light years away from each other. It is about 12 billion years old.

Though it is not a star, Omega Centauri was given a Bayer designation. Unlike other globular clusters, it contains several generations of stars. It has been speculated that Omega Centauri may be the core of a dwarf galaxy several hundred times its present size, which was ripped apart and absorbed by our Milky Way galaxy. Omega Centauri's chemistry and motion in the galaxy is also consistent with this picture. Kapteyn's star which is currently only 13 light years away is thought to originate from Omega Centauri.[9]

Reporting in the April 1, 2008 issue of The Astrophysical Journal, astronomers claimed to have found evidence of a intermediate-mass black hole at the center of Omega Centauri. The observations were made with NASA's Hubble Space Telescope and Gemini Observatory on Cerro Pachon in Chile.[10] Hubble's Advanced Camera for Surveys showed how the stars are bunching up near the center of Omega Centauri, as seen in the gradual increase in starlight near the center. Measuring the speed of the stars swirling near the cluster's center with the Gemini Observatory, the astronomers found that the stars closer to the core are moving faster than the stars farther away. The measurement implies that some unseen matter at the core is tugging on stars near it. By comparing these results with standard models, the astronomers determined that the most likely cause is the gravitational pull of a massive, dense object. They also used models to calculate the black hole's mass.[11]

Like Mayall II, Omega Centauri has a range of metallicities and stellar ages which hints that it did not all form at once (as globular clusters are thought to form) and may in fact be the remainder of the core of a smaller galaxy long since incorporated into the Milky Way.[12]

Small field near center of the cluster taken by HST with its new WFC3 sensor. July 2009

On the 9th September 2009, NASA released the images taken by the Hubble telescope, including NGC 5139. This is one of the first images taken by the new Wide Field Camera 3 (WFC3), installed aboard Hubble in May 2009, during Servicing Mission 4. The camera can snap sharp images over a broad range of wavelengths.[13]

Using the free Stellarium simulation program [14] we can see the location of the globular cluster, from this screenshot. [15]

See also

Wikimedia Commons has media related to Omega Centauri.

References

  1. ^ a b c d "SIMBAD Astronomical Database". Results for NGC 5139. Retrieved 2006-11-16.
  2. ^ a b van de Ven, G.; van den Bosch, R. C. E.; Verolme, E. K.; de Zeeuw, P. T. (January II 2006). "The dynamical distance and intrinsic structure of the globular cluster ω Centauri". Astronomy and Astrophysics. 445 (2): 513–543. doi:10.1051/0004-6361:20053061. best-fit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methods {{cite journal}}: Check date values in: |date= (help)CS1 maint: multiple names: authors list (link)
  3. ^ Omega Centauri - Britannica Online Encyclopedia
  4. ^ Globular cluster NGC 5139
  5. ^ distance × sin( diameter_angle / 2 ), using distance of 5kpc and angle 36.3', = 86 ± 6 ly. radius
  6. ^ "Peering into the Core of a Globular Cluster"[1]
  7. ^ http://www.france-info.com/spip.php?article124990&theme=81&sous_theme=166
  8. ^ Black Hole found in enigmatic Omega Centauri
  9. ^ http://www.newscientist.com/article/mg20427334.100-backward-star-aint-from-round-here.html
  10. ^ http://www.spacetelescope.org/news/html/heic0809.html
  11. ^ Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri Newswise, Retrieved on June 24, 2008.
  12. ^ Hughes, 1999, "G1 in M31 - Giant Age and Metallicity Effects in Omega Centauri I: Stromgren Photometry"
  13. ^ NASA, 2009, "Omega Centauri"
  14. ^ [2]
  15. ^ [3]
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