When Galaxies Collide
Photograph by NASA, H. Ford (JHU), G. Illingworth (USCS/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA
The violent meeting of two galaxies dislodges a tail of stars and gas in a view from the Hubble Space Telescope. The tail is more than 280,000 light-years long, or almost three times the length of the Milky Way. Galaxy collisions play out over hundreds of millions of years. In this one the spiral galaxy UGC 10214, dubbed the Tadpole, broke apart when it was sideswiped by a smaller star system, visible as the blue compact galaxy in the upper left region of the Tadpole. Stars themselves don't crash head-on. It's the gravitational fields of the dark matter and visible matter that get mangled together, throwing stars out of their orbits. Dozens of distant galaxies glint in the background, many of them also in the process of colliding.