A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters are referred to as "super" due to the fact that they are relatively more luminous and contain more mass than other young star clusters. The SSC, however, does not have to physically be larger than other clusters of lower mass and luminosity. They typically contain a very large number of young, massive stars that ionize a surrounding HII region or a so-called "Ultra dense HII regions (UDHIIs)" in the Milky Way Galaxy as well as in other galaxies (however, SSCs do not always have to be inside an HII region). An SSC's HII region is in turn surrounded by a cocoon of dust. In many cases, the stars and the HII regions will be invisible to observations in certain wavelengths of light, such as the visible spectrum, due to high levels of extinction. As a result, the youngest SSCs are best observed and photographed in radio and infrared. SSCs, such as Westerlund 1 (Wd1), have been found in the Milky Way Galaxy. However, most have been observed in farther regions of the universe. In the galaxy M82 alone, 197 young SSCs have been observed and identified using the Hubble Space Telescope.
Generally, SSCs have been seen to form in the interactions between galaxies and in regions of high amounts of star formation with high enough pressures to satisfy the properties needed for the formation of a star cluster. These regions can include newer galaxies with a lot of new star formation, dwarf starburst galaxies, arms of a spiral galaxy that have a high star formation rate, and in the merging of galaxies. In an Astronomical Journal published in 1996, using pictures taken in the ultraviolet (UV) spectrum by the Hubble Space Telescope of star-forming rings in five different barred galaxies, numerous star clusters were found in clumps within the rings which had high rates of star formation. It was found that these clusters had masses of about M☉ to M☉, ages of about 100 Myr, and radii of about 5 pc, and are thought to evolve into globular clusters later in their lifetimes. These properties match those found in SSCs.
The typical characteristics and properties of SSCs:
Given the relatively small size of SSC's compared to their host galaxies, astronomers have had trouble finding them in the past due to the limited resolution of the ground-based and space telescopes at the time. With the introduction of the Hubble Space Telescope (HST) in the 1990s, finding SSC's (as well as other astronomical objects) became much easier thanks to the higher resolution of the HST (angular resolution of ~1/10 arcsecond). This has not only allowed astronomers to see SSC's, but also allowed for them to measure their properties as well as the properties of the individual stars within the SSC. Recently, a massive star, Westerlund 1-26, was discovered in the SSC Westerlund 1 in the Milky Way. The radius of this star is thought to larger than the radius of Jupiter's orbit around the Sun. Essentially, the HST searches the night sky, specifically nearby galaxies, for star clusters and "dense stellar objects" to see if any have the properties similar to that of a SSC or an object that would, in its lifetime, evolve into a globular cluster.
CXOU J164710.2−455216 is an anomalous X-ray pulsar in the massive galactic open cluster Westerlund 1. It is the brightest X-ray source in the cluster, and was discovered
in 2005 in observations made by the Chandra X-ray observatory. The Westerlund 1 cluster is believed to have formed in a single burst of star formation, implying that the progenitor star must have had a mass in excess of 40 solar masses. The fact that a neutron star was formed instead of a black hole implies that more than 95% of the star's original mass must have been lost before or during the supernova that produced the magnetar.On 21 September 2006 the Swift satellite detected a 20ms soft Gamma-ray burst in Westerlund 1. Fortuitously, XMM-Newton observations had been made four days earlier, and repeat observations 1.5 days after the burst revealed the magnetar to be the source of the burst, with the X-ray luminosity increasing by a factor of 100 during the outburst.HD 97950
HD 97950, is a multiple star system and part of a super star cluster within the NGC 3603 H II region. It was catalogued as a single star although it was always known to be a compact cluster. It is now resolved into a massive multiple star at the centre of one of the densest clusters in the galaxy.
Only the six lettered stars A-F at the core of the cluster are typically referred to as components of HD 97950, while the remaining stars of the cluster and surrounding area are usually numbered as members of NGC 3603. The cluster itself is still called the HD 97950 cluster as well as the NGC 3603 young cluster (NGC 3603YC). There are no other notable groupings of stars in NGC 3603 and the HD 97950 cluster is often loosely referred to as simply NGC 3603.Messier 61
Messier 61 (also known as M61 or NGC 4303) is an intermediate barred spiral galaxy in the Virgo Cluster of galaxies. It was discovered by Barnaba Oriani on May 5, 1779. This was six days before Charles Messier observed the same galaxy, but had mistaken it as a comet.NGC 1569
The NGC 1569 is a dwarf irregular galaxy in Camelopardalis. The galaxy is relatively nearby. Consequently, the Hubble Space Telescope can easily resolve the stars within the galaxy. The distance to the galaxy was previously believed to be only 2.4 Mpc (7.8 Mly). However, in 2008 scientists studying images from Hubble calculated the galaxy's distance at nearly 11 million light-years away, about 4 million light-years farther than previous thought: therefore the galaxy resulted to be a member of the IC 342 group of galaxies.NGC 1850
NGC 1850 is a double cluster and a super star cluster in the Dorado constellation, located in the Large Magellanic Cloud at the distance of 168,000 ly (51,510 pc). It was discovered by James Dunlop in 1826. It is an unusual cluster of stars because the distribution of its stars is like a globular cluster, but unlike the globular clusters of the Milky Way it is composed of young stars. The only similar object in the Milky Way is Westerlund 1.NGC 2070
NGC 2070 is a large open cluster and candidate super star cluster located on the south-east corner of the Large Magellanic Cloud. It is located at the centre of the Tarantula Nebula and produces most of the energy that makes it visible. Its central condensation is the star cluster R136, one of the most energetic star clusters known. It holds a number of massive stars, including the most massive star known, R136a1, at 315 M☉ and 8.7 million L☉.NGC 2366
NGC 2366 is a Magellanic barred irregular dwarf galaxy located in the constellation Camelopardalis.There has been confusion about the various components of NGC 2366 and its neighbouring galaxy NGC 2363. At the southern end of NGC 2366 is the large, luminous HII region known as Markarian 71 (Mrk 71).To the west of Mrk 71 is another dwarf galaxy NGC 2363 which is interacting with NGC 2366. Corwins' notes remarks that there are two galaxies with two NGC numbers clearly attached to each one. "We shall just have to get used to calling the HII region "Markarian 71" (or one of its other names) since it is not N2363 as we've thought all these years."Within the region known as Mrk 71, there are two super star clusters (SSC) which are named 'A' and 'B' or 'Knot A' and 'Knot B'.Other names for the above components include: NGC 2366-I, NGC 2366-II, NGC 2366-III, NGC2366-A, NGC 2366-B, NGC 2366-C, NGC 2363-A, NGC 2363-B.NGC 2366 is an outlying member of the M81 Group.NGC 3603
NGC 3603 is a nebula situated in the Carina spiral arm of the Milky Way around 20,000 light-years away from the Solar System. It is a massive HII region containing a very compact open cluster (probably a super star cluster) HD 97950.NGC 4214
NGC 4214 is a dwarf barred irregular galaxy located around 10 million light-years away in the constellation Canes Venatici.NGC 5253
NGC 5253 is an irregular galaxy in the constellation Centaurus. It was discovered by William Herschel on 15 March 1787.NGC 7252
NGC 7252 is a peculiar galaxy resulting from an interaction between two galaxies that started a billion years ago. It is located 220 million light years away in the constellation Aquarius. It is also called Atoms for Peace Galaxy, a nickname which comes from its loop-like structure, made of stars, that resembles a diagram of an electron orbiting an atomic nucleus.Photometric parallax method
The photometric parallax method is a method of data analysis used in astronomy that uses the colours and apparent brightnesses of stars to infer their distances. It was used by the Sloan Digital Sky Survey to discover the Virgo super star cluster.
Unlike the stellar parallax method, photometric parallax can be used to estimate the distances of stars over 10 kpc away, at the expense of much more limited accuracy for individual measurements. Strictly speaking, it does not actually employ any measurements of parallax and can be considered a misnomer.
Assuming that a star is on the main sequence, the star's absolute magnitude can be determined based on its color. Once the absolute and apparent magnitudes are known, the distance to the star can be determined by using the distance modulus.Star cluster
Star clusters are very large groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds to millions of old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.
Star clusters visible to the naked eye include the Pleiades (M45), Hyades, and the Beehive Cluster (M44).Stellar Group
Stellar Group or stellar group may refer to:
CompaniesStellar Group (construction company), of Jacksonville, Florida
a sports management company co-founded by Jonathan BarnettAstronomya grouping of stars
moving group or stellar group, a group of co-moving stars
star cluster, a group of gravitationally bound stars
super star cluster
star cloud, a visually defined patch of stars
asterism (astronomy), a group of stars forming a pattern
multiple star, a set of stars forming a close visual grouping
star system, a gravitationally bound system of starsTrumpler 14
Trumpler 14 (Tr 14) is an open cluster with a diameter of six light-years (1.8 pc), located within the inner regions of the Carina Nebula, approximately 8,980 light-years (2,753 pc) from Earth. Together with the nearby Trumpler 16, they are the main clusters of the Carina OB1 stellar association, which is the largest association in the Carina Nebula, although Trumpler 14 is not as massive or as large as Trumpler 16.About 2000 stars have been identified in Trumpler 14. and the total mass of the cluster is estimated to be 4,300 M☉.Virgo Stellar Stream
The Virgo Stellar Stream, also known as Virgo Overdensity, is the proposed name for a stellar stream in the constellation of Virgo which was discovered in 2005. The stream is thought to be the remains of a dwarf spheroidal galaxy that is in the process of merging with the Milky Way. It is the largest galaxy visible from the Earth, in terms of the area of the night sky covered.
The stream was discovered from photometric data from the Sloan Digital Sky Survey, which was used to create a three-dimensional map of the Milky Way, using the colors and brightness of certain characteristic types of stars to estimate their distance (a method known as "photometric parallax"). The first suggestion of a new galaxy in Virgo was made in 2001 from data obtained as part of the QUEST survey, which used the one-metre Schmidt telescope at the Llano del Hato National Astronomical Observatory in Venezuela to search for RR Lyrae variable stars. Five were found in a clump with a right ascension near 12.4 hours, and the astronomers speculated that this clump was part of a small galaxy being "cannibalised" by the Milky Way.The stream covers over one hundred square degrees and possibly as much as one thousand square degrees (approximately five percent of the hemisphere visible at any one time, or five thousand times the area of the full moon). Despite its proximity to the solar system and the solid angle that it consequently covers, the stream contains only a few hundred thousand stars. The low surface brightness of the galaxy (possibly as low as 32.5 mag/arcmin²) may have militated against its detection in surveys before SDSS. The number of stars in the stream is not greatly in excess of a star cluster, and it has been described by a member of the team that discovered it as "a rather pathetic galaxy" in comparison to the Milky Way. Many of the stars have been known for centuries and thought of as normal Milky Way stars, although they have a lower metallicity than normal Population I stars in the Milky Way.
The stream lies within the Milky Way, approximately 10 kiloparsecs (30,000 light-years) from the Sun, and extending over a region of space at least 10 kpc across in three dimensions. It is close on the plane of the sky to the Sagittarius Dwarf Elliptical Galaxy, which was found in 1994 through a similar photometric analysis of a star survey. The Sagittarius Dwarf is another small galaxy which is also in the process of merging with the Milky Way; however, it is approximately 4 times further away than the stream, so the two are unlikely to be physically related, although it is possible that the Virgo Stellar Stream is a remnant left behind by the disruption of the Sagittarius Dwarf as it had orbited around the Milky Way. The Virgo Stellar Stream also resembles the Monoceros Ring, found in 2002, which has similarly been attributed to the Canis Major Dwarf Galaxy merging with the Milky Way.Westerlund 1
Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster in the Milky Way galaxy, about 3.5–5 kpc away from Earth. It is one of the most massive young star clusters in the Milky Way, and was discovered by Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster.The cluster contains a large number of rare, evolved, high-mass stars, including: 6 yellow hypergiants, 4 red supergiants including Westerlund 1-26, one of the largest known stars, 24 Wolf-Rayet stars, a luminous blue variable, many OB supergiants, and an unusual supergiant sgB[e] star which has been proposed to be the remnant of a recent stellar merger. In addition, X-ray observations have revealed the presence of the anomalous X-ray pulsar CXO J164710.2-455216, a slow rotating neutron star that must have formed from a high-mass progenitor star. Westerlund 1 is believed to have formed in a single burst of star formation, implying the constituent stars have similar ages and compositions.
Aside from hosting some of the most massive and least-understood stars in our galaxy, Westerlund 1 is useful as a relatively nearby, easy to observe super star cluster that can help astronomers determine what occurs within extragalactic super star clusters.Westerlund 1-26
Westerlund 1-26 or Wd 1-26 is a red supergiant or red hypergiant within the outskirts of the Westerlund 1 super star cluster. It is one of the largest known stars discovered so far although its radius is uncertain but is calculated to be between 1,530–2,550 solar radii (1.06×109–1.77×109 km; 7.1–11.9 au), corresponding to a volume between 3.6–16.6 billion times bigger than the Sun. Assuming the upper estimate is correct, if placed at the center of the Solar System, its photosphere would engulf the orbit of Saturn.Westerlund 2
Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The cluster resides inside a stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. It is half a degree from the naked eye Cepheid variable V399 Carinae.
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