NGC 4651: The Umbrella Galaxy

Explanation: Spiral galaxy NGC 4651 is a mere 62 million light-years distant, toward the well-groomed northern constellation Coma Berenices . About the size of our Milky Way, this island universe is seen to have a faint umbrella-shaped structure that seems to extend (left) some 100 thousand light-years beyond the bright galactic disk. The giant cosmic umbrella is now known to be composed of tidal star streams - extensive trails of stars gravitationally stripped from a smaller satellite galaxy. The small galaxy was eventually torn apart in repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. In fact , the picture insert zooms in on the smaller galaxy's remnant core, identified in an extensive exploration of the system , using data from the large Subaru and Keck telescopes on Mauna Kea. Work begun by a remarkable collaboration of amateur and professional astronomers to image faint structures around bright galaxies suggests that even in nearby galaxies , tidal star streams are common markers of such galactic mergers. The result is explained by models of galaxy formation that also apply to our own Milky Way.