elliptical galaxy
Picture a swarm of bees that has settled into a smooth, glowing fuzzball — no spiral arms, no flat disk, just a featureless oval glow that fades from a bright center outward. That is an elliptical galaxy: a system of stars shaped like a ball or a rugby ball, with the stars buzzing around in randomly tilted orbits rather than circling in one neat plane.
Ellipticals are classified E0 to E7, where the number measures how squashed the oval looks (E0 nearly round, E7 strongly flattened). Unlike a spiral, an elliptical has almost no cold gas and dust, so it makes very few new stars; its light comes from old, cool, red stars built long ago. Their stars move on a 'pressure-supported' jumble of orbits — the galaxy holds itself up against gravity by the random speeds of its stars rather than by orderly rotation. Ellipticals span an enormous range: from tiny dwarf ellipticals to the giant cD galaxies at the centers of clusters, some containing trillions of stars across hundreds of thousands of light-years.
Ellipticals matter because they are thought to be the end-products of galactic violence: when two big spirals collide and merge, their orderly disks are scrambled into a single smooth, gas-poor elliptical. They dominate the dense cores of galaxy clusters, follow tight scaling relations like the fundamental plane and the M-sigma relation between their central black hole and their stellar motions, and represent how much of the universe's star formation has already 'switched off' (quenched). A red, dead elliptical is a galaxy that has largely finished building stars.
M87, the giant elliptical at the center of the Virgo cluster, holds several trillion stars and a 6.5-billion-solar-mass black hole — yet from outside it looks like a featureless glowing ellipse, because nearly all its stars are old and red and it makes almost no new ones.
A smooth, gas-poor ball of old red stars — gravity held up by random motion, not rotation.
The E0–E7 number describes only how flattened the galaxy looks from our angle, not its true 3D shape — an elongated elliptical seen end-on can masquerade as a round E0.