What is an elliptical galaxy?

An elliptical galaxy is defined primarily by its ellipsoidal shape, which is more rounded and smooth compared to the structured arms seen in spiral galaxies. One of the key characteristics of elliptical galaxies is their minimal active star formation; they contain older stars and generally have little interstellar gas and dust, which limits the potential for new star creation.

This lack of active star formation is often due to the exhaustion of the materials needed for star creation or the influence of gravitational interactions, which can strip away gas from the galaxy. In contrast, spiral galaxies exhibit distinct spiral arms and are characterized by ongoing star formation within those arms, while galaxies that are actively forming new stars often belong to different classifications, such as starburst galaxies. The description of a galaxy with a flat disk and a bulging center pertains to spiral galaxies, which display a different structural characteristic altogether. Therefore, the choice that identifies an elliptical galaxy as having an ellipsoidal shape and little to no star formation aligns with the established definitions in astronomy.