Galaxies: Islands of Stars in the Universe

Galaxies are vast systems of stars, gas, dust, and dark matter bound together by gravity.
Our Milky Way galaxy contains over 100 billion stars—and likely many more planets.
The Andromeda Galaxy is on a slow-motion collision course with the Milky Way.
Galaxies come in many shapes: spirals, ellipticals, and irregulars.
Dwarf galaxies are small but common, often orbiting larger ones like satellites.
At the heart of most galaxies lies a supermassive black hole.
The largest galaxies can span millions of light-years across.
Galaxies group together in clusters, and clusters form even bigger superclusters.
Observing distant galaxies lets us peer billions of years into the universe’s past.
Galaxies are the building blocks of the cosmos—cosmic islands scattered across the vast sea of space.