What are Shell Elliptical Galaxies
Galaxies come in three main types. One type are the irregular galaxies.these a giant blobs of stars and typical small galaxies. The nest are the spiral galaxies these have a central area with arms spiraling outward, the most famous of these is the Milky Way(us). The next type of galaxy are the elliptical galaxies, if you take a cross section it will look like an ellipse. The largest types of these lay in the middle large of clusters of galaxies and are made from the combination of smaller spiral galaxies. Some these galaxies appear to have shells around them. There are in three dimensions but do not cover the entire galaxy and are bluer than the galaxy they surround which means that they contain a lot of younger stars.
A study of galaxy NGC 3923 using the MegaCam on the CFH telescope in Hawaii has shown this galaxy has 42 shells around it. The team was looking for a shell predicted by MOND but the shell was not there. The team is saying they did not find the shell because the previous observations were in error.