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Overview
A galaxy is a large gravitationally bound system containing stars, gas, dust, stellar remnants, dark matter, and often a central supermassive black hole. Galaxies range from small dwarf galaxies to giant ellipticals and sprawling spirals.
Components
Galaxies contain stars, star clusters, gas clouds, dust, planets, compact remnants, and dark matter halos.
Spiral Galaxies
Spiral galaxies have disks, spiral arms, gas, dust, and ongoing star formation. The Milky Way is a barred spiral galaxy.
Elliptical Galaxies
Elliptical galaxies range from rounded to elongated shapes and often contain older stars with less gas and dust.
Irregular Galaxies
Irregular galaxies lack simple spiral or elliptical shapes and can be shaped by interactions, mergers, or intense star formation.
Dark Matter Halos
Galaxy rotation and gravitational behavior indicate that galaxies are embedded in large dark matter halos.
Galaxy Evolution
Galaxies evolve through star formation, gas inflow, supernova feedback, black hole activity, and mergers.
Common Mistakes
A common mistake is thinking galaxies are only collections of visible stars. Much of their mass appears to be dark matter.
Why This Matters in Physics
Galaxies connect stars, gravity, dark matter, black holes, cosmic structure, and the history of the universe.