Yo Starfriend, I do not know what a shell galaxy is, and while I can guess from the name and the picture, it would be awesome if you could give a description so that the people on this tiny and insignificant speck of stardust can wonder.
Shell galaxies are galaxies with outer shells of dust and gas and stars. Basically they’re characterized by the arcs you see surrounding the underlying galaxy. The structures are three dimensional but not necessarily perfect spheres, which is why “arcs” is a better way to think about it. They are MAYBE a result of galaxy mergers. Also, they happen mostly around elliptical galaxies, and never around spiral galaxies!
Shell galaxies have very amazing and unique shapes. We believe they can be formed by 1 in 3 ways: collisions, companions on radial/nonradial orbits, and mass transfers via rough parabolic encounters.
I want every piece of me to crash into every piece of you,
I swear to god that’s how they make stars.