Giant shells around normal elliptical galaxies

Photographic enhancement of deep 111aJ and 111aF plates taken with the UK Schmidt and Anglo-Australian telescopes have revealed the existence of giant ellipsoidal shells (radii up to 180kpc) within and around the envelopes of several normal elliptical galaxies. It is suggested that these features probably consist of stars and are either the result of a burst of star formation initiated by a powerful shock wave in an intergalactic medium, perhaps during the formation of the galaxies, or are old stars displaced from the nucleus by an explosive event. (UK)