What causes the surrounding shells in peculiar galaxy Cen A? Last month a fascinating image of peculiar galaxy Centaurus A was released [ http://antwrp.gsfc.…], processed to highlight a faint blue arc [ http://www.jhu.edu/…] indicating an ongoing collision with a smaller galaxy. Another interesting feature of Cen A [ http://antwrp.gsfc.…], however, is the surrounding system of shells [ http://www.eso.org/…], better visible here in this recently released wider pan [ http://www.noao.edu…] from the four meter Blanco telescope [ http://www.ctio.noa…] at Cerro Tololo Inter-American Observatory [ http://antwrp.gsfc.…]. Faint shells around galaxies are not unusual and considered by themselves as evidence of a previous galaxy merger [ http://antwrp.gsfc.…], analogous to water ripples [ http://www.colorado…] on a pond. An unexpected attribute [ http://adsabs.harva…] of these shells [ http://zebu.uoregon…] is the abundance of gas, which should become separated from existing stars during the collision [ http://www.astro.qu…].