Omega Centauri
Omega Centauri | |
---|---|
Apparent magnitude (V) | 3.9[4] |
Apparent dimensions (V) | 36′.3[5] |
Physical characteristics | |
Mass | (4.05±0.1)×106[6] M☉ |
Radius | 86 ± 6 ly[7] |
Metallicity | = –1.35 Gyr[8] |
Other designations | NGC 5139,[9] GCl 24,[9] ω Centauri,[3] Caldwell 80, Mel 118 |
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, and a total mass equivalent to 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]
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 rediscovered 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
Properties
At a distance of about 15,800 light-years (4,800 parsecs) from
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.
Evidence of a central black hole
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.[24][25] 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.[24]
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.[26][27] 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.
Disrupted dwarf galaxy
It has been speculated that Omega Centauri is the core of a dwarf galaxy that was disrupted and absorbed by the Milky Way.[28] Indeed, Kapteyn's Star, which is currently only 13 light-years away from Earth, is thought to originate from Omega Centauri.[29] 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.[30]
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.[31]
This cluster figures in the German pulp science-fiction series Perry Rhodan, and a cycle of the spin-off series Atlan, is set in Omega Centauri.
See also
- Canis Major Overdensity
- Fimbulthul stream
- Mayall II
- Messier 54
- NGC 5286
- Sagittarius Dwarf Spheroidal Galaxy
- List of largest known star clusters
References
- Bibcode:1927BHarO.849...11S.
- ^ S2CID 119183070.
- ^ S2CID 15538249.
best-fit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methods
- ^ Skiff, Brian A. (May 2, 1999), "Observational Data for Galactic Globular Clusters", The NGC/IC Project, archived from the original on February 4, 2018, retrieved 2013-08-13.
- ISBN 978-0750306546.
- ^ .
- ^ distance × sin(diameter_angle / 2), using distance of 5 kpc and angle 36.3′, = 86 ± 6 ly radius
- ^ S2CID 51825384.
- ^ a b "NGC 5139". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
- ^ "Omega Centauri: The Largest Globular Cluster". Universe for Facts. Retrieved 21 December 2014.
- ^ "APOD: 2010 March 31 - Millions of Stars in Omega Centauri".
- S2CID 208867075.
- ^ Bayer, Johann (1603). Uranometria (in Latin). Augsburg, [Germany]: Christoph Mang. Available at: Linda Hall Library (University of Missouri (Kansas City, Missouri, US)) Archived 2018-07-24 at the Wayback Machine 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.
- ^ See:
- Halley, Edmond (1716). "An account of several nebualæ or lucid spots like clouds, lately discovered among the fixt stars by help of the telescope". Philosophical Transactions of the Royal Society of London. 29 (347): 390–392. S2CID 186215009. ; see p. 391.
- Reprinted at: SEDS: The Messier Catalog
- Halley, Edmond (1716). "An account of several nebualæ or lucid spots like clouds, lately discovered among the fixt stars by help of the telescope". Philosophical Transactions of the Royal Society of London. 29 (347): 390–392.
- ^ ISBN 978-1107015012.
- ^ 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.
- Bigourdan, G. (1892). "Observations de nébuleuses et d'amas stellaires" [Observations of nebulae and of stellar clusters]. Annales de l'Observatoire de Paris. Observations. 1884. (in French): G-1–G-103. Cheseaux's letter (in French) appears on pp. G-8 – G-9.
- An English translation of Cheseaux's letter appears in: Jones, Kenneth Glyn (1969). "The search for the nebulae - V.". Journal of the British Astronomical Association. 79: 105–112. Bibcode:1969JBAA...79..105J. An English translation of Cheseaux's letter appears on pp. 105–106. Available at: SAO/NASA Astrophysics Data System
- See also: Philippe Loys de Chéseaux (May 4, 1718 – November 30, 1751) at SEDS: The Messier Catalog
- ^ de la Caille (1755). "Sur les étoiles nébuleuses du ciel austral" [On the nebulous stars of the southern sky]. Histoire de l'Académie Royale des Sciences, avec les Mémoires de Mathématique & de Physique (in French). 1755: 194–199. ; 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
- . Omega Centauri is listed as No. 440 on p. 136.
- ^ Harrington, Phil (May 1, 2013), "Binocular Universe: Songs of the Deep South", Cloudy Nights Telescope Reviews, retrieved 2013-08-13.
- ^ a b "Black hole found in Omega Centauri". ESA. 2008-04-02. Retrieved 2009-11-06.
- ^ Frommert, Hartmut; Kronberg, Christine (March 22, 1998), "NGC 5139", The Munich Astro Archive, archived from the original on 2020-06-28, retrieved 2013-08-13.
- ^ a b "Peering into the Core of a Globular Cluster", Hubble Site news Center, October 4, 2001, retrieved 2013-08-13.
- S2CID 119478923.
- ^ S2CID 208867075.
- Bibcode:2008MNSSA..67...82., retrieved 2013-08-13.
- S2CID 15596662.
- S2CID 15235670.
- ^ "Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri" (Press release). 2008-04-02. Retrieved 2009-11-06.
- ^ "Backward star ain't from round here", New Scientist, retrieved 2013-08-13.
- Bibcode:1998AAS...193.6809H.
- ISBN 978-0061840272.
Further reading
- Myeong, G. C.; Evans, N. W.; Belokurov, V.; Sanders, J. L.; Koposov, S. E. (April 2018). "The Shards of ω Centauri". Monthly Notices of the Royal Astronomical Society. .
External links
- Hubblesite - Peering into the core of a globular cluster
- Omega Centauri at Constellation Guide
- Omega Centauri at ESA/Hubble - link not operational Archived 2005-12-27 at the Wayback Machine
- Omega Centauri: Former Core of a Dwarf Galaxy?
- Omega Centauri, Galactic Globular Clusters Database page
- Omega Centauri on
- Omega Centauri on WikiSky - zoomed view
- Omega Centauri: Proud Cluster or Sad Remnant? Archived 2006-05-07 at the Wayback Machine
- SEDS – NGC 5139
- StarDate: Omega Centauri Fact Sheet