About Galaxies
Galaxies are huge systems containing stars, gas, dust, dark matter, planets, and other objects bound together by gravity. They come in many shapes and sizes, and the observable universe contains an immense number of them.
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The Milky Way
Our Solar System is inside a barred spiral galaxy.
Learn MoreSpiral Galaxies
Spiral galaxies have flattened disks, curved arms, and central regions.
Learn MoreElliptical Galaxies
Elliptical galaxies can look like smooth glowing balls or stretched ovals.
Learn MoreIrregular Galaxies
Not every galaxy has a neat spiral or elliptical shape.
Learn MoreGalaxy Collisions
Galaxies can pass through and merge with one another.
Learn MoreGroups and Clusters
Galaxies gather into groups, clusters, and even larger cosmic structures.
Learn MoreCentral Black Holes
Most large galaxies appear to contain supermassive black holes at their centers.
Learn MoreDeep Fields
Long telescope exposures reveal galaxies from the distant universe.
Learn MoreThe Milky Way
The Milky Way contains hundreds of billions of stars and stretches roughly 100,000 light-years across its main disk. Our Solar System is located in a smaller spiral feature called the Orion Spur, far from the galactic center.
Spiral Galaxies
Their arms contain gas, dust, and many young stars. The Milky Way, Andromeda, and Whirlpool are spiral galaxies. The arms are not rigid structures but regions where matter can be compressed and star formation becomes more active.
Elliptical Galaxies
Many contain older stars and relatively little cold gas for new star formation. Some of the most massive known galaxies are giant ellipticals found near the centers of galaxy clusters.
Irregular Galaxies
Irregular galaxies may be distorted by gravitational interactions or may simply lack a strong organized structure. The Large and Small Magellanic Clouds, visible from the Southern Hemisphere, are nearby examples.
Galaxy Collisions
Because stars are separated by enormous distances, individual stars rarely collide during a galaxy merger. Gravity can reshape the galaxies, compress gas, trigger new star formation, and eventually produce a larger combined galaxy.
Groups and Clusters
The Milky Way and Andromeda are part of the Local Group. Larger clusters can contain hundreds or thousands of galaxies. These clusters are connected across the universe by filaments that form part of the cosmic web.
Central Black Holes
The Milky Way's central black hole is called Sagittarius A*. When matter falls toward an actively feeding supermassive black hole, the surrounding region can become extremely bright and produce enormous amounts of radiation.
Deep Fields
Deep-field images stare at a tiny area of sky for a long time. The result can reveal thousands of galaxies, including very distant systems whose light began traveling toward us billions of years ago. Looking far away in space also means looking back in time.