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Topic: Cluster of galaxies

	Hercules Cluster of Galaxies
		This cluster, Abell 2151 in Hercules, is the prototype spiral-rich cluster.
		It is not as rich in galaxies, nor as centrally concentrated, as the Coma cluster.
		Clusters of this kind may be rich in spiral and irregular galaxies, and in Abell 2151 we see many interacting galaxy pairs and small groupings of galaxies.
	www.astr.ua.edu /gifimages/hercules.html (0 words)

	ESA Portal - XMM-Newton mosaics the Coma cluster of galaxies
		Galaxies in the Universe are often to be found in clusters.
		Clusters are also believed to contain, in addition to the baryonic ("ordinary") matter, another component, dark matter whose properties are not well understood and whose presence can probably only be detected by its gravitational influence.
		The orientation of NGC 4839 in the optical coincides with the orientation of the tail.
	www.esa.int /esaCP/GGGWHGUTGEC_index_2.html (0 words)

	The Virgo Cluster of Galaxies
		This giant agglomeration of galaxies is the nearest big cluster of galaxies, the largest proven structure in our intergalactic neighborhood, and the most remote cosmic objects with a physical connection to our own small group of galaxies, the Local Group, including our Milky Way galaxy.
		Our image shows the central portion of the Virgo Cluster of Galaxies, and is centered on the giant elliptical galaxy M87 which is considered to be the dominant galaxy of the whole giant cluster, situated close to its physical center.
		Semi-recent HST observations (from the 1990s) of Cepheids in M100, as well as estimates from the globular cluster luminosity in M87, together with the work of Nial R. Tanvir and, again, HST observations, on the M96 group, extrapolated to this cluster, indicate that the Virgo cluster is at a distance of some 60 million light-years.
	www.seds.org /messier/more/virgo.html (1116 words)

	An Atlas of the Universe - A Glossary
		The term 'cluster' usually refers to a large collection of many tens or hundreds of galaxies and the term 'group' is used for a much smaller grouping.
		Globular clusters usually have a size of 50 to 150 light years and are found scattered in a spherical halo surrounding galaxies.
		The radial velocity of a galaxy caused by the expansion of the universe.
	www.atlasoftheuniverse.com /glossary.html (0 words)

	Galaxy Clusters & Dark Matter
		Clusters can be rich, with several thousand galaxies, or poor, with only 20 or 30 members.
		Clusters of galaxies are classified by their properties;richness (number of members),shape (spherical,flattened, or irregular),and galactic content (spiral-rich,spiral-poor, or elliptical-rich),for example.
		CL 0024+1654 is a large cluster of galaxies located 5 billion light-years from Earth.
	cassfos02.ucsd.edu /public/tutorial/Clusters.html (0 words)

	Deep Sky Terms - Glossary
		Disk Galaxies oriented in space so that they are seen from near their equatorial plane are called "edge-on;" the contrary orientation is called "face-on." Edge-on galaxies look flat and elongated, often with an equatorial dark band or lanes of dust.
		Disk Galaxies oriented in space so that they are seen from near one of their poles are called "face-on;" the contrary orientation is called "edge-on." Face-on galaxies look round and often show structures in their disks prominently, e.g.
		Globular clusters are apparent in all types of galaxies; in disk galaxies, they typically populate the galactic halos.
	www.seds.org /messier/xtra/Terms/dsterms.html (0 words)

	Groups and Clusters of Galaxies
		The galaxies of these groups are in mutual gravitational interaction which may have significant influence on their appearance.
		Big clusters like Virgo have a tendency to attract and finally incorporate the small groups and individual galaxies in their immediate neighborhood as time goes by.
		Besides accumulating mass, the cluster also grows in volume because of the following process: The incoming galaxies are accelerated by the cluster's gravity, and fall in with high velocities.
	www.seds.org /messier/gal_clus.html (0 words)

	Messier Object 49
		Elliptical galaxy Messier 49 (M49, NGC 4472) is one of the brightest member galaxies of the Virgo cluster.
		M49 was the first member of the Virgo cluster of galaxies to be discovered, by Charles Messier, who cataloged it on February 19, 1771.
		M49 is one of the brightest Virgo Cluster member galaxies with its mag 8.5, which corresponds to an absolute magnitude of approximately -22.8, regarding its distance of about 60 million light years.
	www.seds.org /messier/m/m049.html (0 words)

	Messier Object 91
		The barred spiral galaxy M91 is an appealing member of the Virgo Cluster of Galaxies.
		The membership of Messier 91 in the Virgo Cluster of Galaxies was confirmed by a recent measurement of its distance as 52 +/- 6 million light years by detecting Cepheid variables.
		The Discovery of Cepheids in the Virgo Cluster Galaxy NGC 4548.
	www.seds.org /messier/m/m091.html (0 words)

	Jet Propulsion Laboratory
		Marvel at a few gems from the universe, including sparkling clusters of baby stars and the shimmery demise of a dying star.
		The James Webb Space Telescope is designed to study the earliest galaxies and some of the first stars formed after the Big Bang.
		JPL is managing the development of the Mid Infrared Instrument, one of the three focal plane istruments on the infrared space telescope.
	www.jpl.nasa.gov /stars_galaxies (500 words)

	Chandra :: Field Guide to X-ray Sources :: Groups & Clusters of Galaxies
		Galaxy clusters are the largest gravitationally bound objects in the universe.
		Astronomers think that galaxy clusters form as clumps of dark matter and their associated galaxies are pulled together by gravity to form groups of dozens of galaxies, which in turn merge to form clusters of hundreds, even thousands of galaxies.
		The gas in galaxy clusters is heated as the cluster is formed.
	www.chandra.harvard.edu /xray_sources/galaxy_clusters.html (257 words)

	NationMaster - Encyclopedia: Virgo cluster (Site not responding. Last check: )
		The large elliptical galaxy at the centre is the Lenticular Galaxy M84; the elongated image of NGC 4388 (an active spiral galaxy) is in the lower left corner.
		The W cloud is a cloud cluster of galaxies approximately 25-30 megaparsecs distant.
		The large mass of the cluster is indicated by the high peculiar velocities of many of its galaxies, sometimes as high as 1,600 km/s with respect to the cluster's center.
	www.nationmaster.com /encyclopedia/Virgo-cluster (1129 words)

	NationMaster - Encyclopedia: Lenticular galaxy (Site not responding. Last check: )
		The Spindle Galaxy (NGC 5866), a lenticular galaxy in the Draco constellation.
		A lenticular galaxy is a type of galaxy which is an intermediate between an elliptical galaxy and a spiral galaxy in the Hubble sequence classification scheme.
		Lenticular galaxy NGC 5866 in Draco A lenticular galaxy is a type of galaxy which is intermediate between elliptical and spiral in the Hubble sequence classification scheme.
	www.nationmaster.com /encyclopedia/Lenticular-galaxy (551 words)

	Cluster of Galaxies (Site not responding. Last check: )
		Clusters of galaxies, bound ensambles of hundreds of galaxies like our own, are an ideal environment to study galaxy evolution and to learn how this is affected by different physical processes: gravity, starbursts and star formation, interactions with the intergalactic medium and energy emitted from fl holes.
		In the local universe spiral galaxies, gas rich and star forming, are abundant in the low-density field, while S0 and elliptical galaxies (spheroidals with almost no gas and ongoing star formation) dominate the densest regions of the Universe in the cores of galaxy clusters.
		The EDisCS project is the first large systematic explorations of clusters at high redshifts that aims at tracing the evolution of cluster galaxies and clusters between z=0.8 and the present epoch, i.e covering 1/2 of the age of the Universe.
	www.pd.astro.it /oapd/2/2_1/2_1_3/2_1_3_2.html (479 words)

	Colour-Magnitude Relation for Elliptical Galaxies
		Rich cluster of galaxies have central masses of 10,000 × the mass of the Milky Way, and as such are both the most massive collapsed systems and also some of the intrinsically rarest systems in the Universe.
		galaxies are the luminous cluster galaxies (the large interacting spiral in the upper-right hand corner is foreground of the cluster).
		Clusters of galaxies are of particular interest for testing models of galaxy evolution in high density regions.
	www.astro.su.se /~ostlin/ColMag/Source/colMag_clusters.html (822 words)

	Bulletin - 9th June 2006 (Site not responding. Last check: )
		The cluster, which is 10 billion light years from Earth, is also likely to be the most massive yet found at such an early era in the Universe.
		Massive Galaxy Cluster: This image shows the faint galaxies of the cluster in the centre; the fuzzy central area is the X-ray emission from the extremely hot gas that exists between the cluster galaxies
		The galaxy cluster is a fossil of the early Universe and therefore will be treasured by all astronomers.
	www.sussex.ac.uk /press_office/bulletin/09jun06/article1.shtml (476 words)

	Gemini Observatory (Site not responding. Last check: )
		There are now many studies of the distant universe that have explored the formation and evolution of galaxies when the universe was less than half its current age (see related Gemini stories from: January 5, 2004, May 18, 2004 and July 7, 2004).
		Cluster galaxies are older than field galaxies of the same mass, clearly indicating that the high-density environment of the cluster has an impact.
		Thus, the first early-type galaxies that formed in the universe were the most massive ones in galaxy clusters.
	www.gemini.edu /index.php?option=content&task=view&id=197 (835 words)

	Clusters of Galaxies (Site not responding. Last check: )
		Clusters of galaxies are larger than groups, typically containing from about 50 to 1000 members.
		The adjacent image shows the Virgo Cluster of galaxies, which is a nearby rich, irregular cluster that we shall discuss more in the next section.
		In clusters the typical mass to light ratio is ~ 400 in units of solar masses divided by solar luminosities.
	csep10.phys.utk.edu /astr162/lect/gclusters/clusters.html (254 words)

	Universe Today - Galaxy Headed for a Cosmic Collision
		Astronomers think that the galaxy will be completely ripped apart within a billion years, and its stars assimilated into other galaxies in the cluster.
		Under the gravitational grasp of a large gang of galaxies, called the Fornax cluster, the small bluish galaxy is plunging headlong into the group at 600 kilometers per second or nearly 400 miles per second.
		The tidal forces of nearby galaxies in the cluster may also play a role in triggering star formation on such a massive scale.
	www.universetoday.com /am/publish/galaxy_cosmic_collision.html?332005 (670 words)

	Abell cluster
		A rich cluster of galaxies identified in the Abell Catalog of Rich Clusters of Galaxies, which was the first comprehensive catalogue of clusters of galaxies and, in its extended form, is still the largest.
		Abell classified such clusters as regular and irregular, and ranked them on six-point scales according to both their richness (population density) and distance (1 to 6, for closest to furthest).
		Among the best-known Abell clusters are the Perseus Cluster (A426) and the Coma Cluster (A1656).
	www.daviddarling.info /encyclopedia/A/Abell_cluster.html (312 words)

	Discovery of a dark cluster of galaxies
		A model calculation suggested that the quasar might be being lensed by a cluster of galaxies centered in a distant galaxy.
		The total mass of hot gas in a cluster galaxy is now known to exceed the mass of galaxies composing the cluster, on average.
		The X-ray source is clearly extended and the maximum surface brightness is consistent with the position of the optically discovered galaxy, which is thought to be in the center of the lensing cluster of galaxies.
	www.astro.isas.ac.jp /asca/results/dark_cluster-e.html (615 words)

	Too fast, too furious: a galaxy's fatal plunge
		This galaxy took the brunt of the beating as it fell along a trajectory straight through the dense core of the colliding cluster.
		Besides the disrupted features in the galaxy's disk, HST also showed that the light in the tail is mostly attributed to recent star formation, providing a direct link to the stripping of the galaxy as it passed through the cluster core.
		The galaxy C153 is destined to lose the last vestiges of its spiral arms and become a bland S0-type galaxy having a central bulge and disk, but no spiral-arm structure.
	www.physlink.com /News/010604C153.cfm (1251 words)

	Galaxies cluster near dark matter
		To investigate the spatial distribution of galaxies, Farrah used data that recently became available from the Spitzer Wide-area InfraRed Extragalactic (SWIRE) survey, one of the largest such surveys performed by the Spitzer Space Telescope, which was launched in 2003.
		But galaxies themselves often group together into what astronomers call "large-scale structures." And, just as galaxies themselves can take on such shapes as ellipticals and spirals, so, too, can the large-scale structures, ranging from galaxy clusters to long filaments of galaxies to large, empty voids.
		From this he was able to calculate the amount of bunching in candidate galaxy clusters in the early universe.
	www.news.cornell.edu /stories/April06/spatial.clusters.ak.html (576 words)

	Chandra :: Field Guide to X-ray Sources :: Groups & Clusters of Galaxies (Site not responding. Last check: )
		Galaxy clusters are the largest gravitationally bound objects in the universe.
		Astronomers think that galaxy clusters form as clumps of dark matter and their associated galaxies are pulled together by gravity to form groups of dozens of galaxies, which in turn merge to form clusters of hundreds, even thousands of galaxies.
		The gas in galaxy clusters is heated as the cluster is formed.
	chandra.harvard.edu /xray_sources/galaxy_clusters.html (257 words)

	Hubble Heritage
		NGC 3314 lies in Hydra (to be precise, at equinox 2000 coordinates 10 37 12.8 -27 41 04), and at least one of the galaxies is a member of the Hydra I cluster of galaxies (also known as Abell 1060).
		Thus the velocities of both galaxies are consistent with being cluster members in the outer envelope of its velocity range.
		The cluster center lies only 12 minutes of arc away, between the giant elliptical galaxies NGC 3309 and 3311, and just to their east is the giant spiral NGC 3312 (probably a cohort of NGC 3314a, along with the small ringlike galaxy to the east of NGC 3312).
	heritage.stsci.edu /2000/14/supplemental.html (728 words)

	Coma Cluster of Galaxies (Site not responding. Last check: )
		Galaxy Clusters Galaxies, themselves giant assemblies of stars, dust and gas, are collected in clusters containing dozens to thousands of members.
		In this case, the scientists are using giant star clusters in the bright galaxy to gauge the distance to the galaxy cluster.
		Galaxy: a large assembly of gas, dust and millions or billions of stars; seen in different shapes including pinwheelshaped spirals, smooth round ellipticals, and irregulars, having neither spiral arms nor round shape.
	teacherlink.ed.usu.edu /tlnasa/pictures/litho/comacluster (459 words)

	Seeing the invisible — first dark galaxy discovered?
		In the Virgo cluster of galaxies they found a mass of hydrogen atoms a hundred million times the mass of the Sun.
		Astronomers have seen galaxies where the material is moving so fast that they should fly apart — as they don't, there must be a stronger gravitational force acting than can be accounted for using visible matter.
		Dark galaxies are thought to form when the density of matter in a galaxy is too low to create the conditions for star formation.
	www.eurekalert.org /pub_releases/2005-02/ppa-sti022305.php (915 words)

	Clusters of Galaxies
		It is estimated that the composition of a cluster is 10% galaxies, 20% intracluster medium (gas), and 70% dark matter.
		The kinetic energy of the randomly moving galaxies acts like a pressure that balances the force of gravitational attraction, the result is to produce a stable cluster of galaxies.
		In the galaxy evolution panels, each galaxy is weighted by its stellar mass, and the color scale of the images is proportional to the total stellar mass.
	www.universe-review.ca /F04-galactic-cluster.htm (1660 words)

	HI Synthesis of the Hercules Cluster of Galaxies (Site not responding. Last check: )
		Synthesis observations provide complete coverage of the volume of a cluster, we obtain a radio selected catalog of galaxies which is an inventory of all the HI gas in the cluster.
		This project is a demonstration of the power of this technique on the well known Hercules Cluster of galaxies (A2147 and A2151) at z=0.03 using the C and D arrays of the VLA to cover four primary beam areas (about one square degree).
		Hercules is apparently a cluster in which we can trace, from one part to another, the changes of a population of galaxies during the growth of a rich cluster.
	www.aas.org /publications/baas/v26n2/aas184/abs/S6106.html (360 words)

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