Fr.: amas des Arches
One of the three → Galactic center clusters supposed to be the densest young → massive star cluster in the Milky Way. It contains the richest collection of → O stars and → WN Wolf-Rayet stars in any cluster in the Galaxy, thus representing the largest collection of the most massive stars in the Galaxy. With its estimated age of 2-3 million years, the Arches cluster is the youngest of the massive clusters in the Galactic center. → Quintuplet cluster; → Central cluster (Figer et al. 2002, ApJ 581, 258; and 1999, ApJ 525, 750).
Arches, from the presence of Galactic center thermal → arched filaments, about 100 → light-years in projection from the Galactic center (Morris & Yusef-Zadeh, 1985, AJ 90, 2511), from M.E. arche, O.Fr. arche "arch of a bridge," from L. arcus, → arc; → cluster.
Fr.: amas de la ruche
Fr.: amas lié
A cluster of astronomical objects, such as stars or galaxies, held together by their mutual gravitational attraction. → bound system.
Fr.: amas de Brocchi
Same as the → Coathanger and Collinder 399.
Named after the American amateur astronomer D. F. Brocchi who created a map of the cluster in the 1920s for calibrating photometers; → cluster.
Fr.: amas de la Balle, ~ du Boulet
A → cluster of galaxies at a → redshift of z = 0.296 undergoing a violent → merger process nearly in the → plane of the sky. Also known as 1E 0657-558. The head-on collision between the main cluster and a subcluster ramming with an apparent speed of about 4700 km s-1 occurred about 150 x 106 years ago. The two clusters are currently moving away from each other while the space between them is filled with a very hot gas (first observed in X-rays by → Chandra) resulting from the overheating due to the collision. The Bullet cluster has the highest X-ray luminosity and temperature of all known clusters. The X-ray gas of the bullet (amounting to 2 x 1013 solar masses) collides with the X-ray gas of the main cluster (1014 solar masses) and forms a well defined → supersonic (Mach 3) → bow shock. A significant offset between the distribution of X-ray emission and the mass distribution has been observed, and diversely interpreted.
The name Bullet refers to the smaller subcluster, that has created the bow shock; → cluster.
Fr.: superamas du Centaur
The nearest large → supercluster. It is dominated by the → galaxy cluster A3526 (→ Abell catalog). The Centaurus supercluster is a long structure that stretches away from us. The most distant of the clusters, A3581, is about 300 million → light-years away.
Fr.: amas central
One of the three obscured → Galactic center clusters, which contains the supermassive black hole → Sgr A*. The first stars observed in the Central cluster were evolved → massive stars showing strong He I emission lines (2.058 microns) in the near infrared K band. Subsequently more than 80 massive stars were detected including various types of → Wolf-Rayet stars, as well as → O-type and → B-type → supergiants and → dwarfs (see, e.g. Martins et al. 2007, A&A 468, 233).
1) xušé (#); 2) xušé bastan (#)
Fr.: 1) amas; 2) s'agglomérer, se grouper
1) A group of the same astronomical objects gathered or occurring closely
together, such as → cluster of galaxies,
→ globular cluster, → open cluster,
and so on.
O.E. clyster "cluster," probably akin to O.E. clott "clot".
Xušé "cluster, a bunch of grapes, an ear of corn," (Laki huša), from Mid.Pers. hošag or xušak; cf. Skt. guccha- "bundle, bunch of flowers, cluster of blossom, clump;" xušé bastan, with bastan "to bind, shut; to clot; to form seed buds", from Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie," Skt. bandh- "to bind, tie, fasten," PIE *bhendh- "to bind," cf. Ger. binden, E. bind.
Fr.: cœur d'amas
The central part of a cluster (globular, galaxies, etc.) where the spatial density of the objects making up the cluster is much higher than the average value.
cluster mass function (CMF)
karyâ-ye jerm-e xušé
Fr.: fonction de masse d'amas
An empirical power-law relation representing the number of clusters as a function of their mass. It is defined as: N(M)dM ∝ M -αdM, where the exponent α has an estimated value of about 2 and dM is the mass interval. It is believed that this is a universal law applying to a variety of objects including globular clusters, massive young clusters, and H II regions.
cluster of galaxies
xuše-ye kahkašâni (#)
Fr.: amas de galaxies
Same as → galaxy cluster.
Fr.: agglomération, groupement
Grouping of a number of similar astronomical objects.
Noun from verb → cluster.
qânun-e xušé bandi
Fr.: loi de groupement
An empirical power-law representing the number of stellar clusters as a function of the number of stars per cluster within an interval. It is expressed as: N(N*) dN*∝ N*-α dN*, where N(N*) is the number of clusters containing N* stars and dN* is the interval in star number. It is believed that this relationship applies to a variety of systems, including stellar clusters, globular clusters, H II regions (Oey et al. 2004, AJ 127, 1632).
xuše-ye Gisu (#)
Fr.: amas de Coma
The nearest rich cluster of galaxies which contains more than a thousand known galaxies, is about 20 million light-years in diameter, and lies about 280 million light-years away in the → constellation → Coma Berenices. Also known as Abell 1656.
Fr.: amas de Fourneau
Galactic center cluster
xuše-ye markaz-e kahkešân
Fr.: amas du centre galactique
One of the three massive clusters located toward the → Galactic center: → Quintuplet cluster, → Arches cluster, → Central cluster. Heavily extinguished by the presence of dust clouds and only accessible at infrared (and longer) wavelengths or in X-rays, each of these clusters has a population of more than a hundred → massive stars. The three clusters are similar in most respects, each containing about 104 solar masses in stars. The Arches cluster is younger than the two others.
xuše-ye kahkešâni, ~ kahkešânhâ
Fr.: amas galactique
xuše-ye kahkašâni (#)
Fr.: amas de galaxies
An aggregation of galaxies, made up of a few to a few thousand members, which may or may not be held together by its own gravity. Same as → cluster of galaxies.
xuše-ye guysân (#)
Fr.: amas globulaire
A spherical aggregate of stars made up of thousands to a few million stars which is an orbiting satellite of a galaxy. There are over 150 globular clusters orbiting our galaxy. Globular clusters are gravitationally → bound systems, highly concentrated to the center (up to a few 103 stars per cubic → light-years), with a volume ranging from a few dozen up to more than 300 light-years in diameter. They are generally old and → metal-poor and are among the first objects to be formed in a galaxy. There is also strong evidence that they form in major galaxy interactions and → mergers. The stars in a globular cluster are thought to have a common origin and thus a single age and → chemical abundance; with some exceptions such as → Omega Centauri and NGC 2808, which exhibit multiple populations. The presence of various sub-populations within a globular cluster is interpreted as indicating distinct epochs of mass → accretion and/or major → star formation. The Milky Way hosts about 200 globular clusters. They are spherically distributed about the → Galactic Center up to a radius of 350 light-years, with a maximum concentration toward the Galactic center. All but the smallest → dwarf galaxies possess globular clusters. Some galaxies, e.g. M87, contain several thousands of them. There are, however, important differences. While all the globular clusters in our Galaxy and in → M31 are old (ages of about 10 billion years, at least), there are galaxies, such as the two → Magellanic Clouds and → M33, that host much younger globular clusters (ages of a few billion years, or less).
Xušé, → cluster; guysân "shaped like a globe," from guy, → globe + -sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career").
xuše-ye Herâkles, ~ Herkul
Fr.: amas d'Hercule
A small, irregular → cluster of galaxies with fewer than 100 galaxies in its core. It has no strongly dominant central galaxy and is notable for the high proportion of spirals. It lies some 500 million → light-years away in the constellation → Hercules; also known as Abell 2151.