Section: STEM · AstronomyDifficulty: Easy
Galaxy
USUK
A gravitationally bound system of stars, gas, dust, and dark matter.
Also: island universe
Definition
A galaxy is a gravitationally bound system containing stars, stellar remnants, interstellar gas and dust, and dark matter. Galaxies range in size from dwarf galaxies with a few hundred million stars to giant galaxies with hundreds of trillions of stars. They come in various morphologies: elliptical, spiral, and irregular. The observable universe contains an estimated two trillion galaxies.
Example
“The Milky Way is a barred spiral galaxy containing about 200-400 billion stars, including our Sun, which orbits the galactic center at about 230 km/s, taking approximately 225 million years to complete one orbit.”
Synonyms
- star system
- stellar system
- island universe
Images
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