Lone stars.Call them outcasts, label them nomads. They're stars without a home galaxy, and for the first time astronomers have spied hundreds of them adrift in the Virgo cluster Virgo cluster Closest large cluster of galaxies at a distance of about 50 million light-years in the direction of the constellation Virgo. About 200 bright galaxies and thousands of faint ones reside in the cluster. , a collection of galaxies some 60 million light-years from Earth. Each isolated star is gravitationally grav·i·ta·tion n. 1. Physics a. The natural phenomenon of attraction between physical objects with mass or energy. b. The act or process of moving under the influence of this attraction. 2. bound to the cluster as a whole but not to any particular galaxy among the 2,500 in Virgo. Harry C. Ferguson of the Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). in Baltimore, Nial Tanvir of the University of Cambridge in England, and Ted von Hippel of the University of Wisconsin-Madison “University of Wisconsin” redirects here. For other uses, see University of Wisconsin (disambiguation). A public, land-grant institution, UW-Madison offers a wide spectrum of liberal arts studies, professional programs, and student activities. found the stars by aiming the Hubble Space Telescope's wide-field and planetary camera at a seemingly blank area near the center of the cluster. By comparing the number of stars in this field to the number in an image of the Hubble Deep Field The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, based on the results of a series of observations by the Hubble Space Telescope. It covers an area 144 arcseconds across, equivalent in angular size to a tennis ball at a distance of 100 , a region devoid of nearby clusters, Ferguson and his collaborators counted about 600 homeless stars and deduced that as many as 10 million others, too faint for Hubble to detect, may reside at Virgo's center. A trillion stars similar in mass to the sun may roam the vast emptiness of intergalactic space in Virgo, the team estimates. This population could account for 10 percent of the Virgo cluster's mass. Another team used the Anglo-American Telescope in Coonabarabran, Australia, to observe planetary nebulas, or clouds of gas ejected from dying stars, in the Virgo and Fornax clusters. These scientists estimate that intergalactic in·ter·ga·lac·tic adj. Being or occurring between galaxies: intergalactic space. in stars make up 40 percent of the mass of a cluster. The existence of homeless stars is no surprise, says Ferguson. For years, astronomers have searched for such stars, believed to have been tossed out of their birth galaxies by collisions, mergers, or simply close encounters with other galaxies in the cluster. Diffuse, excess light recorded by ground-based telescopes hinted at a population of roaming stars in Virgo This is the list of notable stars in the constellation Virgo, sorted by decreasing brightness. Name Designation Location Magnitude Dist. (ly) Sp. class Notes B F HD HIP RA Dec vis. abs. Spica α 67 116658 65474 13h 25m 11. . Ferguson notes that most of the stars seen by Hubble appear to be unusually bright red giants. These elderly stars have a uniform brightness. They may thus offer a new way to estimate the distance to Virgo, a stepping-stone to determining the size and age of the universe, Ferguson says. In addition, the number of these stars and their distribution throughout the cluster may help trace the vast amount of invisible material, or dark matter, thought to reside in Virgo. |
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