Astronomy:Omega Centauri

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Omega Centauri
File:300px
The globular cluster Omega Centauri
Observation data (J2000 epoch)
ClassVIII[1]
ConstellationCentaurus
Right ascension 13h 26m 47.28s[2]
Declination−47° 28′ 46.1″[2]
Distance15.8 ± 1.1 kly (4.84 ± 0.34 kpc)[3]
Apparent magnitude (V)3.9[4]
Apparent dimensions (V)36′.3[5]
Physical characteristics
Mass(4.05±0.1)×106[6] M☉
Radius86 ± 6 ly[7]
Metallicity[Fe/H] = –1.35[8] dex
Estimated age11.52 Gyr[8]
Other designationsNGC 5139,[9] GCl 24,[9] ω Centauri,[3] Caldwell 80, Mel 118
See also: Globular cluster, List of globular clusters

Omega Centauri (ω Cen, NGC 5139, or Caldwell 80) is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 17,090 light-years (5,240 parsecs), it is the largest known globular cluster in the Milky Way at a diameter of roughly 150 light-years.[10] It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses,[11] making it the most massive known globular cluster in the Milky Way.

Omega Centauri is very different from most other galactic globular clusters to the extent that it is thought to have originated as the core remnant of a disrupted dwarf galaxy.[12] There is evidence of an intermediate-mass black hole in the dense core of this cluster, although this is disputed.

Observation history

Around 150 AD, Greco-Roman writer and astronomer Ptolemy catalogued this object in his Almagest as a star on the centaur's back, "Quae est in principio scapulae". German cartographer Johann Bayer used Ptolemy's data to designate this object "Omega Centauri" with his 1603 publication of Uranometria.[13] Using a telescope from the South Atlantic island of Saint Helena, English astronomer Edmond Halley observed this object in 1677, listing it as a non-stellar object. In 1716, it was published by Halley among his list of six "luminous spots or patches" in the Philosophical Transactions of the Royal Society.[14][15]

Swiss astronomer Jean-Philippe de Cheseaux included Omega Centauri in his 1746 list of 21 nebulae,[15][16] as did French astronomer Lacaille in 1755, whence the catalogue number is designated L I.5.[17] It was first recognized as a globular cluster by Scottish astronomer James Dunlop in 1826, who described it as a "beautiful globe of stars very gradually and moderately compressed to the centre".[18][19]

Properties

At a distance of about 17,000 light-years (5,200 parsecs) from Earth, Omega Centauri is one of the few globular clusters visible to the naked eye—and appears almost as large as the full Moon when seen from a dark, rural area.[20] It is the brightest, largest and, at 4 million solar masses,[6] the most massive-known globular cluster associated with the Milky Way. Of all the globular clusters in the Local Group of galaxies, only Mayall II in the Andromeda Galaxy is brighter and more massive.[21] Orbiting through the Milky Way, Omega Centauri contains several million Population II stars and is about 12 billion years old.[22]

The stars in the core of Omega Centauri are so crowded that they are estimated to average only 0.1 light-year away from each other.[22] The internal dynamics have been analyzed using measurements of the radial velocities of 469 stars.[23] The members of this cluster are orbiting the center of mass with a peak velocity dispersion of 7.9 km s−1. The mass distribution inferred from the kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity distribution.[citation needed]

Members

These stars are the well studied members of the cluster. Some are abundant in metals and elements. (eg. Iron, Carbon, Oxygen)[24][25]

Star Name Spectral
type 		Star Type
Central Black Hole BH(IMBH) Intermediate Mass Black Hole
Variable Star 2 Template:StarM Red Giant

M type AGB Variable (Semi Regular)

Variable Star 6 Template:StarM Red Giant

M type AGB Variable (Semi Regular)

Variable Star 42 Template:StarM Red Giant

M type AGB Variable (Semi Regular)

Variable Star 147 Template:StarM Red Giant

M type AGB Variable (Semi Regular)

ROA 102 Template:StarM Red Giant

M type RGB

Omega Centauri 65 Template:StarK Orange Giant

K type RGB

Omega Centauri 74 Template:StarK Orange Giant

K type RGB

Omega Centauri 91 Template:StarK Orange Giant

K type RGB

Omega Centauri 101 Template:StarK Orange Giant

K type RGB

Star #124 Template:StarK Orange Giant

K type RGB

ROA 24 Template:StarK Orange Giant

K type RGB

ROA 46 Template:StarK Orange Giant

K type RGB

ROA 65 Template:StarK Orange Giant

K type RGB

ROA 74 Template:StarK Orange Giant

K type RGB

ROA 91 Template:StarK Orange Giant

K type RGB

ROA 101 Template:StarK Orange Giant

K type RGB

ROA 123 Template:StarK Orange Giant

K type RGB

ROA 139 Template:StarK Orange Giant

K type RGB

ROA 256 Template:StarK Orange Giant

K type RGB

ROA 270 Template:StarK Orange Giant

K type RGB

ROA 276 Template:StarK Orange Giant

K type RGB

ROA 577 Template:StarK Orange Giant

K type RGB

(An unnamed star) Template:StarK Orange Giant

K type RGB Red Straggler CH Star

Variable Star 1 Template:StarG Yellow Giant

Variable (RR Lyrae type)

Variable Star 15 Template:StarG Yellow Giant
ROA 279 Template:StarG Yellow Giant

Common stars in the cluster

These are the common or notable types of stars in the cluster. For the binary stars, the spectral class here is the primary stars’ spectral class.

Star Name Spectral
type
Red Giants

(M type RGB)

Template:StarM
Red Giants

(M type AGB)

Template:StarM
Orange Giants

(K type RGB)

Template:StarK
Yellow Giants Template:StarG
Template:StarF
Blue Giants Template:StarB
Main Sequence Stars Template:StarB
Template:StarA
Template:StarF
Template:StarG
Template:StarK
Semi-Regular Variables Template:StarM
Template:StarK
Irregular Variables Template:StarM
Template:StarK
Carbon Stars Template:StarM
Zirconium(S type) Stars Template:StarM
CH Stars Template:StarK
Red Stragglers Template:StarK
Symbiotic binaries Template:StarK
Population II Cepheids Template:StarK
Template:StarG
Eclipsing Binaries Template:StarM
Template:StarK
Template:StarG
Subgiants Template:StarK
Template:StarG
RR Lyrae Variables Template:StarG
Template:StarF
Template:StarA
Blue Stragglers Template:StarA
Template:StarB
SX Phoenicis Variables Template:StarA
Template:StarF
BY Draconis Variables Template:StarG
Template:StarK
Template:StarM
Cataclysmic Variables Template:StarK
Template:StarM
Red dwarfs Template:StarM
Blue Subdwarfs Template:StarB
Stellar remnants

(White Dwarfs, Neutron Stars, Stellar Black Holes)

D/WD/VII

NS BH (SBH)

Evidence of a central black hole

The central region of Omega Centauri. The lower illustration charts the future positions of the stars highlighted by the white box in the top image. Each streak represents the star's predicted motion over the next 600 years. The period between dots corresponds to 30 years. October 2010

A 2008 study presented evidence for an intermediate-mass black hole at the center of Omega Centauri, based on observations made by the Hubble Space Telescope and Gemini Observatory on Cerro Pachón in Chile.[26][27] Hubble's Advanced Camera for Surveys showed that stars are bunching up near the center of Omega Centauri, as evidenced by the gradual increase in starlight near the center. Using instruments at the Gemini Observatory to measure the speed of stars swirling in the cluster's core, E. Noyola and colleagues found that stars closer to the core are moving faster than stars farther away. This measurement was interpreted to mean that unseen matter at the core is interacting gravitationally with nearby stars. By comparing these results with standard models, the astronomers concluded that the most likely cause was the gravitational pull of a dense, massive object such as a black hole. They calculated the object's mass at 40,000 solar masses.[26]

More recent work has challenged conclusions that there is a black hole in the cluster's core, in particular disputing the proposed location of the cluster center.[28][29] Calculations using a revised location for the center found that the velocity of core stars does not vary with distance, as would be expected if an intermediate-mass black hole were present. The same studies also found that starlight does not increase toward the center but instead remains relatively constant. The authors noted that their results do not entirely rule out the black hole proposed by Noyola and colleagues, but they do not confirm it, and they limit its maximum mass to 12,000 solar masses.

A study from July 10, 2024 has examined seven fast-moving stars from the center of Omega Centauri and found that their speeds were consistent with an intermediate-mass black hole of at least 8,200 solar masses[30], but this conclusion was again questioned in a later study[31]

Disrupted dwarf galaxy

Captured with the WFI camera from ESO's La Silla Observatory

It has been speculated that Omega Centauri is the core of a dwarf galaxy that was disrupted and absorbed by the Milky Way.[32][33] Indeed, Kapteyn's Star, which is currently only 13 light-years away from Earth, is thought to originate from Omega Centauri.[34] Omega Centauri's chemistry and motion in the Milky Way are also consistent with this picture.[20] Like Mayall II, Omega Centauri has a range of metallicities and stellar ages that suggests 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.[35]

In fiction

The novel Singularity (2012), by Ian Douglas, presents as fact that Omega Centauri and Kapteyn's Star originate from a disrupted dwarf galaxy, and this origin is central to the novel's plot. A number of scientific aspects of Omega Centauri are discussed as the story progresses, including the likely radiation environment inside the cluster and what the sky might look like from inside the cluster.[36]

The character Atlan has adventures in Omega Centauri in cycle 7 of the Atlan series, a spinoff of the German science fiction series Perry Rhodan.[37]

See also

References

  1. ↑ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin 849 (849): 11–14, Bibcode: 1927BHarO.849...11S. 
  2. ↑ 2.0 2.1 Goldsbury, Ryan et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal 140 (6): 1830–1837, doi:10.1088/0004-6256/140/6/1830, Bibcode: 2010AJ....140.1830G. 
  3. ↑ 3.0 3.1 van de Ven, G.; van den Bosch, R. C. E.; Verolme, E. K.; de Zeeuw, P. T. (2 January 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. Bibcode: 2006A&A...445..513V. "best-fit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methods". 
  4. ↑ Skiff, Brian A. (May 2, 1999), "Observational Data for Galactic Globular Clusters", The NGC/IC Project, http://www.ngcicproject.org/papers/gctext.htm, retrieved 2013-08-13. 
  5. ↑ Arnold, H. J. P.; Doherty, Paul; Moore, Patrick (1999), The Photographic Atlas of the Stars, CRC Press, p. 173, ISBN 978-0750306546, https://books.google.com/books?id=YjcvJUfnWBAC&pg=PA173. 
  6. ↑ 6.0 6.1 D'Souza, Richard; Rix, Hans-Walter (March 2013), "Mass estimates from stellar proper motions: the mass of ω Centauri", Monthly Notices of the Royal Astronomical Society 429 (3): 1887–1901, doi:10.1093/mnras/sts426, Bibcode: 2013MNRAS.429.1887D. 
  7. ↑ distance × sin(diameter_angle / 2), using distance of 5 kpc and angle 36.3′, = 86 ± 6 ly radius
  8. ↑ 8.0 8.1 Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society 404 (3): 1203–1214, doi:10.1111/j.1365-2966.2010.16373.x, Bibcode: 2010MNRAS.404.1203F. 
  9. ↑ 9.0 9.1 "NGC 5139". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+5139. 
  10. ↑ "Omega Centauri: The Largest Globular Cluster". http://www.universeforfacts.com/2013/11/omega-centauri-largest-globular-cluster.html. 
  11. ↑ "APOD: 2010 March 31 - Millions of Stars in Omega Centauri". http://apod.nasa.gov/apod/ap100331.html. 
  12. ↑ Noyola, Eva; Gebhardt, Karl; Bergmann, Marcel (2008). "Gemini and Hubble Space Telescope Evidence for an Intermediate Mass Black Hole in omega Centauri". The Astrophysical Journal 676 (2): 1008. doi:10.1086/529002. Bibcode: 2008ApJ...676.1008N. 
  13. ↑ Bayer, Johann (1603) (in la). Uranometria. Augsburg, [Germany]: Christoph Mang.  Available at: Linda Hall Library (University of Missouri (Kansas City, Missouri, US)) The pages of this book are not numbered. However, towards the end of the book there appears "Tabula quadragesima prima, Centaurus." (Forty-first table, Centaur). The table lists Omega Centauri as "21 ω In imo dorso" (21 ω At the bottom of the back). The following page shows the constellation Centaur and Omega Centauri as a star labelled ω at the base of the Centaur's back.
  14. ↑ See:
  15. ↑ 15.0 15.1 O'Meara, Stephen James (2013), Deep-Sky Companions: Southern Gems, Cambridge University Press, p. 244, ISBN 978-1107015012, Bibcode: 2013dcsg.book.....O, https://books.google.com/books?id=S5QIEKns33sC&pg=PA244. 
  16. ↑ Cheseaux compiled a list of nebulae during 1745–1746. He sent the list to his grandfather, in the form of a letter. The letter was read before the French Academy of Sciences in 1746. However, it was first published only in 1892 as part of a large article by the French astronomer Guillaume Bigourdan.
  17. ↑ de la Caille (1755). "Sur les étoiles nébuleuses du ciel austral" (in fr). Histoire de l'Académie Royale des Sciences, avec les Mémoires de Mathématique & de Physique 1755: 194–199. https://www.biodiversitylibrary.org/item/88652#page/394/mode/1up.  ; see in the table on p. 196: "Nébuleuse du Centaure ... " Note: The catalog number "L I.5" designates: that the nebula is listed in Lacaille's catalog of 1755 (hence the "L"); that Omega Centauri is a nebula of the "first type" (première espèce, namely, nebulae that do not seem to be accompanied by stars when viewed via a telescope that is 2 feet long; hence the Roman numeral "I"); and that Omega Centauri is listed fifth among the nebulae of the first type (hence the "5"). See: Deep Sky Observer's Companion – the online database
  18. ↑ Dunlop, J. (1828). "A catalogue of nebulae and clusters of stars in the southern hemisphere, observed at Parramatta in New South Wales". Philosophical Transactions of the Royal Society 118: 113–151. doi:10.1098/rstl.1828.0010. Bibcode: 1828RSPT..118..113D. https://babel.hathitrust.org/cgi/pt?id=hvd.hxkbyy&view=1up&seq=133.  Omega Centauri is listed as No. 440 on p. 136.
  19. ↑ Harrington, Phil (May 1, 2013), "Binocular Universe: Songs of the Deep South", Cloudy Nights Telescope Reviews, http://www.cloudynights.com/item.php?item_id=2871, retrieved 2013-08-13. 
  20. ↑ 20.0 20.1 "Black hole found in Omega Centauri". ESA. 2008-04-02. http://www.esa.int/esaSC/SEMPGM5QGEF_index_0.html. 
  21. ↑ Frommert, Hartmut; Kronberg, Christine (March 22, 1998), "NGC 5139", The Munich Astro Archive, http://www.maa.clell.de/Messier/E/Xtra/NGC/n5139.html, retrieved 2013-08-13. 
  22. ↑ 22.0 22.1 "Peering into the Core of a Globular Cluster", Hubble Site news Center, October 4, 2001, http://hubblesite.org/newscenter/archive/releases/2001/33/image/a/, retrieved 2013-08-13. 
  23. ↑ Merritt, David; Meylan, Georges; Mayor, Michel (September 1997). "The stellar dynamics of Omega Centauri". The Astrophysical Journal 114: 1074–1086. doi:10.1086/118538. Bibcode: 1997AJ....114.1074M. 
  24. ↑ Johnson, Christian I.; Pilachowski, Catherine A. (October 2010). "Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)" (in en). The Astrophysical Journal 722 (2): 1373–1410. doi:10.1088/0004-637X/722/2/1373. ISSN 0004-637X. https://ui.adsabs.harvard.edu/abs/2010ApJ...722.1373J/abstract. 
  25. ↑ Jofré, P.; Aguilera-Gómez, C.; Villarreal, P.; Cubillos, F. A.; Das, P.; Hua, X.; Yates, R.; Silva, P. et al. (July 2025). "Studying stellar populations in Omega Centauri with phylogenetics" (in en). Astronomy and Astrophysics 699: A291. doi:10.1051/0004-6361/202554863. ISSN 0004-6361. https://ui.adsabs.harvard.edu/abs/2025A&A...699A.291J/abstract. 
  26. ↑ 26.0 26.1 Noyola, E.; Gebhardt, K.; Bergmann, M. (April 2008). "Gemini and Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in ω Centauri". The Astrophysical Journal 676 (2): 1008–1015. doi:10.1086/529002. Bibcode: 2008ApJ...676.1008N. 
  27. ↑ Noyola, Eva; Christensen, Lars Lindberg; Villard, Ray; Michaud, Peter (April 2, 2008), "Black hole found in enigmatic Omega Centauri", Monthly Notes of the Astronomical Society of South Africa 67 (5–6): 82, Bibcode: 2008MNSSA..67...82., http://www.spacetelescope.org/news/heic0809/, retrieved 2013-08-13. 
  28. ↑ Anderson, J.; van der Marel, R. P. (February 2010). "New Limits on an Intermediate-Mass Black Hole in Omega Centauri. I. Hubble Space Telescope Photometry and Proper Motions". The Astrophysical Journal 710 (2): 1032–1062. doi:10.1088/0004-637X/710/2/1032. Bibcode: 2010ApJ...710.1032A. 
  29. ↑ van der Marel, R. P.; Anderson, J. (February 2010). "New Limits on an Intermediate-Mass Black Hole in Omega Centauri. II. Dynamical Models". The Astrophysical Journal 710 (2): 1063–1088. doi:10.1088/0004-637X/710/2/1063. Bibcode: 2010ApJ...710.1063V. 
  30. ↑ Haberle, Maximiliam; and 17 others (10 July 2024). "Fast-moving stars around an intermediate-mass black hole in Omega Centauri". Nature 631 (8020): 285–288. doi:10.1038/s41586-024-07511-z. PMID 38987499. Bibcode: 2024Natur.631..285H. 
  31. ↑ Bañares-Hernández, Andrés; Calore, Francesca; Martin Camalich, Jorge; Read, Justin (2025), "New constraints on the central mass contents of ω Centauri from combined stellar kinematics and pulsar timing", Astronomy & Astrophysics 693: 104, doi:10.1051/0004-6361/202451763, Bibcode: 2025A&A...693A.104B 
  32. ↑ Bekki, Kenji; Freeman, Ken (2013), "Formation of ω Centauri from an ancient nucleated dwarf galaxy in the young Galactic disc", Monthly Notices of the Royal Astronomical Society 346: L11, doi:10.1046/j.1365-2966.2003.07275.x, Bibcode: 2003MNRAS.346L..11B 
  33. ↑ "Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri" (Press release). 2008-04-02. Retrieved 2009-11-06.
  34. ↑ "Backward star ain't from round here", New Scientist, https://www.newscientist.com/article/mg20427334.100-backward-star-aint-from-round-here.html, retrieved 2013-08-13. 
  35. ↑ Hughes, J. D.; Wallerstein, G. (December 1998), "Age and Metallicity Effects in Omega Centauri I: Stromgren Photometry", Bulletin of the American Astronomical Society 30: 1348, Bibcode: 1998AAS...193.6809H. 
  36. ↑ Douglas, Ian (2012). Singularity. Harper Voyager. ISBN 978-0061840272. 
  37. ↑ "Centauri (Zyklus) – Perrypedia". https://www.perrypedia.de/wiki/Centauri_(Zyklus). 

Further reading

Coordinates: Sky map 13h 26m 45.89s, −47° 28′ 36.7″



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