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. It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses , making it the most massive known globular cluster in the Milky Way.
35-500: 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 . 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 . Using
70-520: A blue compact dwarf galaxy ( BCD galaxy ) is a small galaxy which contains large clusters of young, hot, massive stars . These stars, the brightest of which are blue, cause the galaxy itself to appear blue in colour. Most BCD galaxies are also classified as dwarf irregular galaxies or as dwarf lenticular galaxies . Because they are composed of star clusters, BCD galaxies lack a uniform shape. They consume gas intensely, which causes their stars to become very violent when forming. BCD galaxies cool in
105-520: A blue compact dwarf galaxy ( BCD galaxy ) is a small galaxy which contains large clusters of young, hot, massive stars . These stars, the brightest of which are blue, cause the galaxy itself to appear blue in colour. Most BCD galaxies are also classified as dwarf irregular galaxies or as dwarf lenticular galaxies . Because they are composed of star clusters, BCD galaxies lack a uniform shape. They consume gas intensely, which causes their stars to become very violent when forming. BCD galaxies cool in
140-636: 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. 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. Dwarf galaxy A dwarf galaxy
175-539: A few hundred to one hundred thousand stars , making them the faintest galaxies in the Universe . UFDs resemble globular clusters (GCs) in appearance but have very different properties. Unlike GCs, UFDs contain a significant amount of dark matter and are more extended. UFDs were first discovered with the advent of digital sky surveys in 2005, in particular with the Sloan Digital Sky Survey (SDSS). UFDs are
210-423: A few hundred to one hundred thousand stars , making them the faintest galaxies in the Universe . UFDs resemble globular clusters (GCs) in appearance but have very different properties. Unlike GCs, UFDs contain a significant amount of dark matter and are more extended. UFDs were first discovered with the advent of digital sky surveys in 2005, in particular with the Sloan Digital Sky Survey (SDSS). UFDs are
245-518: A much later time than the ancient UFDs. These galaxies have not been observed in our Universe so far. Ultra-compact dwarf galaxies (UCD) are a class of very compact galaxies with very high stellar densities, discovered in the 2000s. They are thought to be on the order of 200 light years across, containing about 100 million stars. It is theorised that these are the cores of nucleated dwarf elliptical galaxies that have been stripped of gas and outlying stars by tidal interactions , travelling through
280-518: A much later time than the ancient UFDs. These galaxies have not been observed in our Universe so far. Ultra-compact dwarf galaxies (UCD) are a class of very compact galaxies with very high stellar densities, discovered in the 2000s. They are thought to be on the order of 200 light years across, containing about 100 million stars. It is theorised that these are the cores of nucleated dwarf elliptical galaxies that have been stripped of gas and outlying stars by tidal interactions , travelling through
315-649: 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 . Swiss astronomer Jean-Philippe de Cheseaux included Omega Centauri in his 1746 list of 21 nebulae , as did French astronomer Lacaille in 1755, whence
350-575: Is M60-UCD1 , about 54 million light years away, which contains approximately 200 million solar masses within a 160 light year radius; the stars in its central region are packed 25 times more densely than stars in Earth's region in the Milky Way. M59-UCD3 is approximately the same size as M60-UCD1 with a half-light radius , r h , of approximately 20 parsecs but is 40% more luminous with an absolute visual magnitude of approximately −14.6. This makes M59-UCD3
385-475: Is M60-UCD1 , about 54 million light years away, which contains approximately 200 million solar masses within a 160 light year radius; the stars in its central region are packed 25 times more densely than stars in Earth's region in the Milky Way. M59-UCD3 is approximately the same size as M60-UCD1 with a half-light radius , r h , of approximately 20 parsecs but is 40% more luminous with an absolute visual magnitude of approximately −14.6. This makes M59-UCD3
SECTION 10
#1733084556225420-883: Is a small galaxy composed of about 1000 up to several billion stars , as compared to the Milky Way 's 200–400 billion stars. The Large Magellanic Cloud , which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition. One theory states that most galaxies, including dwarf galaxies, form in association with dark matter , or from gas that contains metals. However, NASA 's Galaxy Evolution Explorer space probe identified new dwarf galaxies forming out of gases with low metallicity . These galaxies were located in
455-415: Is about 12 billion years old. 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. The internal dynamics have been analyzed using measurements of the radial velocities of 469 stars. The members of this cluster are orbiting the center of mass with a peak velocity dispersion of 7.9 km s. The mass distribution inferred from
490-500: The Dark Ages within the first billion years after the Big Bang . More than 20 known dwarf galaxies orbit the Milky Way, and recent observations have also led astronomers to believe the largest globular cluster in the Milky Way, Omega Centauri , is in fact the core of a dwarf galaxy with a black hole at its centre, which was at some time absorbed by the Milky Way. In astronomy ,
525-399: The Dark Ages within the first billion years after the Big Bang . More than 20 known dwarf galaxies orbit the Milky Way, and recent observations have also led astronomers to believe the largest globular cluster in the Milky Way, Omega Centauri , is in fact the core of a dwarf galaxy with a black hole at its centre, which was at some time absorbed by the Milky Way. In astronomy ,
560-526: The Leo Ring , a cloud of hydrogen and helium around two massive galaxies in the constellation Leo . Because of their small size, dwarf galaxies have been observed being pulled toward and ripped by neighbouring spiral galaxies , resulting in stellar streams and eventually galaxy merger . There are many dwarf galaxies in the Local Group ; these small galaxies frequently orbit larger galaxies, such as
595-423: The Leo Ring , a cloud of hydrogen and helium around two massive galaxies in the constellation Leo . Because of their small size, dwarf galaxies have been observed being pulled toward and ripped by neighbouring spiral galaxies , resulting in stellar streams and eventually galaxy merger . There are many dwarf galaxies in the Local Group ; these small galaxies frequently orbit larger galaxies, such as
630-636: The Milky Way , the Andromeda Galaxy and the Triangulum Galaxy . A 2007 paper has suggested that many dwarf galaxies were created by galactic tides during the early evolutions of the Milky Way and Andromeda. Tidal dwarf galaxies are produced when galaxies collide and their gravitational masses interact . Streams of galactic material are pulled away from the parent galaxies and the halos of dark matter that surround them. A 2018 study suggests that some local dwarf galaxies formed extremely early, during
665-519: The Milky Way , the Andromeda Galaxy and the Triangulum Galaxy . A 2007 paper has suggested that many dwarf galaxies were created by galactic tides during the early evolutions of the Milky Way and Andromeda. Tidal dwarf galaxies are produced when galaxies collide and their gravitational masses interact . Streams of galactic material are pulled away from the parent galaxies and the halos of dark matter that surround them. A 2018 study suggests that some local dwarf galaxies formed extremely early, during
700-650: The Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition. One theory states that most galaxies, including dwarf galaxies, form in association with dark matter , or from gas that contains metals. However, NASA 's Galaxy Evolution Explorer space probe identified new dwarf galaxies forming out of gases with low metallicity . These galaxies were located in
735-455: The Milky Way are also consistent with this picture. 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. The novel Singularity (2012), by Ian Douglas , presents as fact that Omega Centauri and Kapteyn's Star originate from
SECTION 20
#1733084556225770-417: 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 . 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. Calculations using a revised location for the center found that
805-420: The catalogue number is designated L I.5. 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". 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
840-436: 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. It has been speculated that Omega Centauri is the core of a dwarf galaxy that was disrupted and absorbed by the Milky Way. Indeed, Kapteyn's Star , which is currently only 13 light-years away from Earth, is thought to originate from Omega Centauri. Omega Centauri's chemistry and motion in
875-538: 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,
910-418: The full Moon when seen from a dark, rural area. It is the brightest, largest and, at 4 million solar masses , 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. Orbiting through the Milky Way, Omega Centauri contains several million Population II stars and
945-758: The hearts of rich clusters. UCDs have been found in the Virgo Cluster , Fornax Cluster , Abell 1689 , and the Coma Cluster , amongst others. In particular, an unprecedentedly large sample of ~ 100 UCDs has been found in the core region of the Virgo cluster by the Next Generation Virgo Cluster Survey team. The first ever relatively robust studies of the global properties of Virgo UCDs suggest that UCDs have distinct dynamical and structural properties from normal globular clusters. An extreme example of UCD
980-522: The hearts of rich clusters. UCDs have been found in the Virgo Cluster , Fornax Cluster , Abell 1689 , and the Coma Cluster , amongst others. In particular, an unprecedentedly large sample of ~ 100 UCDs has been found in the core region of the Virgo cluster by the Next Generation Virgo Cluster Survey team. The first ever relatively robust studies of the global properties of Virgo UCDs suggest that UCDs have distinct dynamical and structural properties from normal globular clusters. An extreme example of UCD
1015-521: The kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity distribution. 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. Hubble's Advanced Camera for Surveys showed that stars are bunching up near
1050-409: The most dark matter -dominated systems known. Astronomers believe that UFDs encode valuable information about the early Universe , as all UFDs discovered so far are ancient systems that have likely formed very early on, only a few million years after the Big Bang and before the epoch of reionization . Recent theoretical work has hypothesised the existence of a population of young UFDs that form at
1085-409: The most dark matter -dominated systems known. Astronomers believe that UFDs encode valuable information about the early Universe , as all UFDs discovered so far are ancient systems that have likely formed very early on, only a few million years after the Big Bang and before the epoch of reionization . Recent theoretical work has hypothesised the existence of a population of young UFDs that form at
Omega Centauri - Misplaced Pages Continue
1120-410: The process of forming new stars . The galaxies' stars are all formed at different time periods, so the galaxies have time to cool and to build up matter to form new stars. As time passes, this star formation changes the shape of the galaxies. Nearby examples include NGC 1705 , NGC 2915 , NGC 3353 and UGCA 281 . Ultra-faint dwarf galaxies (UFDs) are a class of galaxies that contain from
1155-410: The process of forming new stars . The galaxies' stars are all formed at different time periods, so the galaxies have time to cool and to build up matter to form new stars. As time passes, this star formation changes the shape of the galaxies. Nearby examples include NGC 1705 , NGC 2915 , NGC 3353 and UGCA 281 . Ultra-faint dwarf galaxies (UFDs) are a class of galaxies that contain from
1190-475: The second densest known galaxy. Based on stellar orbital velocities, two UCD in the Virgo Cluster are claimed to have supermassive black holes weighing 13% and 18% of the galaxies' masses. Dwarf galaxy A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars , as compared to the Milky Way 's 200–400 billion stars. The Large Magellanic Cloud , which closely orbits
1225-512: 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
#224775