Shell galaxy

Shell galaxies were discovered in 1979 by David Malin. They are elliptical galaxies surrounded by thin shells of stars which are thought to have been ejected during a galaxy merger . They are different from ring galaxies in that the shells surrounding the elliptical galaxies and are much further away from the galaxy's centre and much fainter than the rings. Spectroscopyof the stars in the shell show that they are old whereas the stars in a ring galaxy are young.