In the late 1920s, Edwin Hubble discovered that the universe is expanding. His study of distant galaxies revealed that the wavelength of the light received from them has been shifted toward the red end of the spectrum. This "redshift," a type of Doppler effect, indicates that almost every galaxy is moving away from us at a rate roughly proportional to its distance. In addition to the expansion velocity, all galaxies have a relatively small "peculiar velocity." The peculiar velocity is the motion of the galaxy through space that is not associated with the expansion of the universe. This motion may be caused by the gravitational attraction of neighboring galaxies and matter.
During the 1980s, a group of astronomers, dubbed the "Seven Samurai," examined these peculiar velocities and determined that a "Great Attractor" is pulling on every galaxy within a region of space 300 million light-years across. The Great Attractor is believed to be located in the direction of the constellation Virgo. The local galaxies, including the Milky Way, appear to be rushing toward it at approximately 700 kilometers per second. On the opposite side of the Great Attractor, the Samurai have identified several galaxies moving toward us, which indicates that the source of the gravitational pull is a relatively small, supermassive object.
Great Attractor - basic info about the GA
* Photo credit - A. Sandage (Carnegie Observatories), A. Saha (Space Telescope Science Institute), G.A. Tammann, and L. Labhardt (Astronomical Institute, University Basel), F.D. Macchetto and N. Panagia (Space Telescope Science Institute/ European Space Agency), and NASA
