Star clusters are groups of stars which are gravitationally bound. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth Gravitation is a natural Phenomenon by which objects with Mass attract one another Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. An open cluster is a group of up to a few thousand Stars that were formed from the same Giant molecular cloud, and are still loosely gravitationally 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. Gravitation is a natural Phenomenon by which objects with Mass attract one another See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter A stellar association is a very loose Star cluster, looser than both Open clusters and Globular clusters Stellar associations will normally contain from
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Globular Cluster
Globular clusters, or GC, are roughly spherical groupings of from 10,000 to several million stars packed into regions of from 10 to 30 light years across. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by They commonly consist of very old Population II stars -- just a few hundred million years younger than the universe itself -- which are mostly yellow and red, weighing a bit less than two solar masses. In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. Such stars predominate within clusters because hotter and more massive stars have exploded as supernovae, or evolved through planetary nebula phases to end as white dwarfs. A supernova (plural supernovae or supernovas) is a stellar Explosion. A planetary nebula is an Emission nebula consisting of a glowing shell of Gas and plasma formed by certain types of Stars when they die A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. Yet a few rare blue stars exist in globulars, thought to be formed by stellar mergers in their dense inner regions; these stars are known as blue stragglers. Blue stragglers ( BSS) are Stars in open or Globular clusters that are hotter and bluer than other cluster stars having the same Luminosity
In our galaxy, globular clusters are distributed roughly spherically in the galactic halo, around the galactic centre, orbiting the centre in highly elliptical orbits. The Galactic Center is the rotational center of the Milky Way Galaxy. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In 1917, the astronomer Harlow Shapley was able to estimate the Sun's distance from the galactic centre based on the distribution of globular clusters; previously the Sun's location within the Milky Way was by no means well established. Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena Harlow Shapley ( November 2 1885 &ndash October 20 1972) was an American Astronomer. The Sun (Sol is the Star at the center of the Solar System. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply
Until recently, globular clusters were the cause of a great mystery in astronomy, as theories of stellar evolution gave ages for the oldest members of globular clusters that were greater than the estimated age of the universe. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime However, greatly improved distance measurements to globular clusters using the Hipparcos satellite and increasingly accurate measurements of the Hubble constant resolved the paradox, giving an age for the universe of about 13 billion years and an age for the oldest stars of a few hundred million years less. Hipparcos (an Acronym for Hi gh P recision Par allax Co llecting S atellite) was an Astrometry mission Hubble's law is the statement in Physical cosmology that the Redshift in light coming from distant galaxies is proportional to their distance A paradox is a true statement or group of statements that leads to a Contradiction or a situation which defies intuition; or inversely
Super star clusters, such as Westerlund 1 in the Milky Way, may be the precursors of globular clusters. A super star cluster ( SSC) is a very large region of Star formation thought to be the precursor of a Globular cluster Westerlund 1 (sometimes Wd1) is the most massive compact young Star cluster in the Local group and is about 5 kpc away [1]
Our galaxy has about 150 globular clusters, some of which may have been captured from small galaxies disrupted by the Milky Way, as seems to be the case for the globular cluster M79. Messier 79 (also known as M79 or NGC 1904) is a Globular cluster in the Lepus constellation. Some galaxies are much richer in globulars: the giant elliptical galaxy M87 contains over a thousand. An elliptical galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble (whose name was dedicated Messier 87 (also known as M87, Virgo A or NGC 4486) is a giant Elliptical galaxy.
A few of the brightest globular clusters are visible to the naked eye, with the brightest, Omega Centauri, having been known since antiquity and catalogued as a star before the telescopic age. The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or Omega Centauri or NGC 5139 is a Globular cluster of Stars seen in the constellation of Centaurus, discovered by Edmond Halley in The best known globular cluster in the northern hemisphere is M13 (modestly called the Great Globular Cluster in Hercules). The Great Globular Cluster in Hercules (also known as the Hercules Globular Cluster, Messier Object 13, Messier 13, M13, or NGC 6205 The Great Globular Cluster in Hercules (also known as the Hercules Globular Cluster, Messier Object 13, Messier 13, M13, or NGC 6205
Intermediate forms
In 2005, astronomers discovered a completely new type of star cluster in the Andromeda Galaxy, which are, in several ways, very similar to globular clusters (although less dense). Currently, there are not any intermediate clusters (also known as extended globular clusters) discovered in the Milky Way. The three discovered in Andromeda Galaxy are M31WFS C1 [1], M31WFS C2, & M31WFS C3. The Andromeda Galaxy (ænˈdrɒmədə also known as Messier 31, M31, or NGC 224; often referred to as the Great Andromeda
These new-found star clusters contain hundreds of thousands of stars, a similar number of stars that can be found in globular clusters. The clusters also share other characteristics with globular clusters, e. g. the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across – and hundreds of times less dense. The distances between the stars are, therefore, much greater within the newly discovered extended clusters. Parametrically, these clusters lie somewhere between a (low dark-matter) globular cluster and a (dark matter-dominated) dwarf spheroidal galaxy. Dwarf spheroidal galaxy ( dSph) is a term in Astronomy applied to low luminosity Galaxies that are Companions to the Milky [2]
How these clusters are formed is not yet known, but their formation might well be related to that of globular clusters. Why M31 has such clusters, while the Milky Way has not, is not yet known. It is also unknown if any other galaxy contains this kind of clusters, but it would be very unlikely that M31 is the sole galaxy with extended clusters. [2]
Open clusters
Open clusters, (OC) are very different from globular clusters. An open cluster is a group of up to a few thousand Stars that were formed from the same Giant molecular cloud, and are still loosely gravitationally Unlike the spherically-distributed globulars, they are confined to the galactic plane, and are almost always found within spiral arms. The galactic coordinate system is a Celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy A spiral galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the They are generally young objects, up to a few tens of millions of years old. They form from H II regions such as the Orion Nebula. An H II region (also known as Emission nebula) is a cloud of glowing Gas and plasma, sometimes several hundred Light-years across The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a Diffuse nebula situated south of Orion 's Belt
Open clusters usually contain up to a few hundred members, within a region up to about 30 light-years across. Being much less densely populated than globular clusters, they are much less tightly gravitationally bound, and over time, are disrupted by the gravity of giant molecular clouds and other clusters. See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar Close encounters between cluster members can also result in the ejection of stars, a process known as 'evaporation'.
The most prominent open clusters are the Pleiades and Hyades in Taurus. The Pleiades (ˈpliːədiːz or /ˈplaɪədiːz/ also known as M 45, the '''Seven Sisters''', Seven Stars, SED, Matariki The Hyades ( Greek Ὑάδες also known as Melotte 25 or Collinder 50 or Caldwell 41 is the nearest Open cluster to the Taurus (it looks like a bull (ˈtɔrəs bull, symbol, Unicode ♉ is one of the Constellations of the Zodiac. The Double Cluster of h+Chi Persei can also be prominent under dark skies. The Double Cluster is the common name for the naked-eye open clusters NGC 884 and NGC 869, which are close together in the constellation Perseus NGC 869 is an Open cluster located 6800 Light years ref name="Kharchenko" /> away in the constellation of Perseus. NGC 884 is an Open cluster located 7600 Light years ref name="Kharchenko" /> away in the constellation of Perseus. Open clusters are often dominated by hot young blue stars, because although such stars are short-lived in stellar terms, only lasting a few tens of millions of years, open clusters tend to have dispersed before these stars die.
Super star cluster
Super star cluster, (SSC) is a very large region of star formation thought to be the precursor of a globular cluster. A super star cluster ( SSC) is a very large region of Star formation thought to be the precursor of a Globular cluster
Embedded cluster
Embedded clusters, (EC) are stellar clusters that are partially or fully incased in an Interstellar dust or gas. The most famous example of an embedded cluster is the Trapezium cluster. The Trapezium, or Orion Trapezium Cluster is a tight Open cluster of Stars that lies within the heart of the Orion Nebula, in the Constellation In ρ Ophiuchi cloud (L1688) core region has an embedded cluster. [2]
Stellar associations
Once an open cluster has become gravitationally unbound, the constituent stars will continue to move on similar paths through space. The group is then known as a stellar association, or a moving group. Most of the stars in the Big Dipper are members of a former open cluster, the Ursa Major Moving Group, and have similar proper motions. This article is about the asterism; for other uses see Big Dipper (disambiguation. The Ursa Major Moving Group, also known as Collinder 285, is the closest Moving group to Earth, that is a set of stars with common velocities in space The proper motion of a Star is the measurement of its change in position in the sky over time after Improper motions are accounted for Other stars across the sky, including Alphecca and Zeta Trianguli Australis, are related to this group. Alpha Coronae Borealis (α CrB / α Coronae Borealis is a Binary star in the Constellation Corona Borealis. Zeta Trianguli Australis (ζ TrA is a Spectroscopic binary in the Constellation Triangulum Australe. The Sun lies at the edge of this stream of stars at the moment, but isn't a member as is shown by its different galactic orbit, age, and chemical composition. The Sun (Sol is the Star at the center of the Solar System.
Another stellar association is that surrounding Mirfak (α Persei), which is very prominent in binoculars. Alpha Persei (α Per is the brightest Star in the Constellation of Perseus, just outshining the constellation's best known star Algol. For other meanings see Perseus (disambiguation Perseus (ˈpɝsiːəs or /-sjuːs/ is a northern Constellation, named after the Greek Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and Distant moving clusters can't readily be detected since the proper motions of the stars need to be known.
Astronomical significance of clusters
The study of star clusters is very important in many areas of astronomy. Because the stars were all born at roughly the same time, the different properties of all the stars in a cluster are a function only of mass, and so stellar evolution theories rely on observations of open and globular clusters.
Clusters are also a crucial step in determining the distance scale of the universe. The cosmic distance ladder (also known as the Extragalactic Distance Scale) is the succession of methods by which astronomers determine the Distances to celestial A few of the nearest clusters are close enough for their distances to be measured using parallax. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between A Hertzsprung-Russell Diagram can be plotted for these clusters which has absolute values known on the luminosity axis. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a colour-magnitude diagram, or CMD Luminosity has different meanings in several different fields of science Then, when similar diagram is plotted for a cluster whose distance is not known, the position of the main sequence can be compared to that of the first cluster and the distance estimated. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness This process is known as main-sequence fitting. Reddening and stellar populations must be accounted for when using this method. Extinction is a term used in Astronomy to describe the absorption and Scattering of Electromagnetic radiation emitted by Astronomical objects In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen
References
- ^ "ESO", Young and Exotic Stellar Zoo: ESO's Telescopes Uncover Super Star Cluster in the Milky Way, 2005-03-22. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 238 - Gordian I and his son Gordian II are proclaimed Roman emperor. Retrieved on 2007-03-20. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1600 - The Linköping Bloodbath takes place on Maundy Thursday in Linköping, Sweden.
- ^ a b A. P. Huxor, N. R. Tanvir, M. J. Irwin, R. Ibata (2005). "A new population of extended, luminous, star clusters in the halo of M31". Monthly Notices of the Royal Astronomical Society 360: 993-1006. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
See also
- Protostar
- Star cluster Hodge 301
- Stellar associations
- Robust Associations of Massive Baryonic Objects (RAMBOs)
External links
- NGC 2419 -Globular Claster on SKY-MAP. A protostar is a large object that forms by contraction out of the gas of a Giant molecular cloud in the Interstellar medium. Hodge 301 is a Star cluster in the Tarantula Nebula, visible from Earth's Southern Hemisphere. A stellar association is a very loose Star cluster, looser than both Open clusters and Globular clusters Stellar associations will normally contain from In astronomy a RAMBO or robust association of massive baryonic objects is a dark cluster made of Brown dwarfs or White dwarfs. ORG
- Star Clusters, SEDS Messier pages
- RG Research: Embedded Clusters
- Encyclopaedia Britannica, Star cluster - full article
- Super Star Cluster Discovered in Our Own Milky Way
- Probing the Birth of Super Star Clusters: Implications for Massive Star Formation, Kelsey E. Johnson, 2005
- A new population of extended, luminous star clusters in the halo of M31, A. P. Huxor et al. , 2004
- HST/NICMOS Observations of the Embedded Cluster in NGC 2024: Constraints on the IMF and Binary Fraction, Wilson M. Liu et al. , 2003
- The Discovery of an Embedded Cluster of High-Mass Stars Near SGR 1900+14, Frederick J. Vrba et al. , 2000
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