Elliptical galaxy
An elliptical galaxy is a galaxy with a smooth, ellipsoidal stellar distribution, little interstellar gas or dust, and mostly old stars.
Galaxy morphology: The classification of galaxies by their visible structure and shape. Elliptical galaxies are one major form in the classification of galaxy shapes.
Galaxy merger: An interaction in which two or more galaxies combine through gravity. Major mergers can scramble stellar orbits and produce an elliptical remnant.
Spiral galaxy: A galaxy with a flattened rotating disk, often containing spiral arms, gas, dust, and young stars. Its organized disk and active star formation contrast with the smooth, gas-poor elliptical form.
M87: A giant elliptical galaxy at the center of the Virgo Cluster. Its enormous stellar extent and central black hole make it a prominent giant elliptical.
Hubble sequence: A scheme that organizes galaxies by morphology, including ellipticals, spirals, and lenticulars. It places ellipticals within a broader system for comparing galaxy forms.
Dynamical relaxation: The evolution of a gravitational system toward a more stable statistical state through interactions among its constituents. Relaxation helps explain the smooth stellar distributions left by violent assembly.
Lenticular galaxy: A disk galaxy with a central bulge and a smooth disk, but no prominent spiral arms. It can resemble an elliptical while retaining a disk that distinguishes its structure.
Centaurus A: A nearby peculiar galaxy with an elliptical-like body crossed by a prominent dust lane. Its unusual dust lane exposes how mergers can leave complex features in an elliptical system.
Stellar population: A group of stars characterized by shared properties such as age, chemical composition, or motion. The stars in ellipticals are predominantly old compared with those in actively star-forming galaxies.
Violent relaxation: Rapid redistribution of stellar energies during a changing gravitational potential, especially in a merger. It can erase ordered structure as an elliptical galaxy forms.