The source of a great attraction.The source of a great attraction The Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. and its galactic neighbors appear caught up in the irresistible gravitational 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. pull of a vast agglomeration ag·glom·er·a·tion n. 1. The act or process of gathering into a mass. 2. A confused or jumbled mass: of matter whose center lies about 150 million light-years away. Known as the Great Attractor Great Attractor Proposed concentration of mass, equivalent to tens of thousands of galaxies, that influences the movement of many galaxies, including the Milky Way Galaxy (see galaxy). , the concentration of mass significantly alters the rate of which these galaxies spread apart as the universe expands. Alan M. Dressler of the Pasadena, Calif.-based Observatories of the Carnegie Institution of Washington  The introduction to this article may be too long. Please help improve the introduction by moving some material from it into the body of the article according to the suggestions at and Sandra M. Faber Sandra Moore Faber (1944 - ) is a University Professor of Astronomy and Astrophysics at the University of California, Santa Cruz and works at the Lick Observatory. In 1972 she received her Ph.D. in Astronomy from Harvard University, prior to that she obtained a B.A. of the University of California, Santa Cruz The University of California, Santa Cruz, also known as UC Santa Cruz or UCSC, is a public, collegiate university, one of the ten campuses of the University of California. , have now amassed sufficient data to confirm that Great Attractor's existence and to define its extent. Working independently, Robert A. Schommer of Rutgers University in New Brunswick, N.J., and his colleagues have obtained similar results. Dressler and Faber were members of the international team of astronomers that first identified a strong local perturbation perturbation (pŭr'tərbā`shən), in astronomy and physics, small force or other influence that modifies the otherwise simple motion of some object. The term is also used for the effect produced by the perturbation, e.g. in the smooth outward flow of matter associated with the universe's expansion (SN: 3/22/86, p. 182). Galaxies in a large region of space seemed to be streaming in the general direction of a collection of galaxies known as the Hydra-Centaurus supercluster. There entire region was expanding less rapidly than the universe as a whole, suggesting the presence of an unidentified center of attraction somewhere beyond the Hydra-Centaurus galaxies. But the original measurements of galactic distances and velocities did not extend as far as the postulated attractor's center, where gravity would pull equally in all directions and any galaxies present would have no motion beyond that associated with the expansion of space. "We had walked on the side of a [cloud-enshrouded] mountain and inferred its presence without seeing its peak," Dressler says. The new measurements by the two research groups include galaxies that appear to lie near the attractor's center. A few of the galaxies even seem to be falling toward Earth, indicating they sit on the attractor's far side. These data enable astronomers to establish the attractor's sphere of influence. By almost any measure, the Great Attractor represents the dominant structure in our part of the universe. Roughly spherical, it stretches 300 million light-year across the sky and contains a mass equivalent to tens of thousands of galaxies. But its enormous gravitational influence results not so much from its large mass density as from its vast extent. Compared with some galactic superclusters, "it's not a particularly dense structure," Dressler says. "It's just very big." The Milky Way itself is actually inside but on the edge of the Great Attractor. The new data also seem to rule out the presence of an even stronger attractor just beyond the Great Attractor. Astronomers have detected concentrations of galaxies that lie farther out farther out Of or relating to an option contract with a later expiration date than a contract that is currently owned or being considered. For example, a contract with a May expiration date is farther out than a contract with a February expiration date of (SN: 4/15/89, p. 230), but these concentrations don't appear to influence galactic motion in the vicinity of the Great Attractor. Nevertheless, astronomers suspect that features on the scale of the Great Attractor are common in the universe. "We found one . . . after sampling only a small fraction of the universe," Dressler notes. |
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