An elliptical galaxy is a type of galaxy characterized by its elliptical shape, composition, and origin.
Key Characteristics of Elliptical Galaxies
Elliptical galaxies differ significantly from spiral galaxies. Here's a breakdown of their defining features:
- Shape: They exhibit an elliptical or near-spherical shape. Unlike spiral galaxies, they lack spiral arms.
- Composition:
- Stars: Primarily composed of old, red stars.
- Gas and Dust: Contain very little gas and dust. This absence of raw material limits new star formation.
- Stellar Orbits: The stars within an elliptical galaxy have random orbits in multiple planes, contributing to its overall shape.
- Formation: Elliptical galaxies are believed to form through the merging or collision of other galaxies. According to provided context, "an elliptical galaxy is one that was created when other galaxies collided".
Comparison with Spiral Galaxies
| Feature | Elliptical Galaxy | Spiral Galaxy |
|---|---|---|
| Shape | Elliptical or spherical | Disc-shaped with spiral arms |
| Star Population | Primarily old, red stars | Mixture of old and young stars |
| Gas & Dust | Very little | Abundant |
| Star Formation | Low or non-existent | Active |
| Stellar Orbits | Random, multi-planar | Organized, mostly within the galactic plane |
| Formation | Galaxy Mergers | Gradual growth or minor mergers |
Origin of Elliptical Galaxies
The dominant theory suggests that elliptical galaxies are formed through the merger of two or more galaxies. When galaxies collide, their gravitational interactions disrupt their structures, leading to a redistribution of stars and gas. The collision can strip away the gas and dust that are crucial for forming new stars, leaving behind a galaxy primarily composed of older stars in a spheroidal shape.
