Giant shells around normal elliptical galaxies

Malin, D.F. & Carter, D. 1980, Nature 285, 643.

Photographic enhancement of deep IIIaJ and IIIaF plates taken with the UK Schmidt and Anglo-Australian telescopes reveals the existence of giant ellipsoidal shells within and around the envelopes of several normal elliptical galaxies. The dimensions of these features are vast; they occur at radii of up to 180 kpc (assuming H(0) = 50 km/s Mpc). It is reported 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.