Formation and Evolution of Galaxies

Part of Hall of the Universe.

Formation and evolution of the galaxies_HERO AMNH/D. Finnin

In the early universe, there were no galaxies. Today, there are many billions. How did they form? Astronomers use the fundamental laws of physics to deduce the basic story of galaxy formation. Galaxies form out of immense clouds of gas that collapse and rotate. As they evolve, stars form within them. Entire galaxies can collide, changing their appearance. Looking deep into space, we see galaxies at earlier stages in their lives, and learn more about their evolution. They are more numerous, display unusual shapes, and have episodes of energetic outbursts. Galaxies can be seen back to more than 10 billion years ago.

location (galaxies)
processes in galaxy formation - cosmic web
On scales much larger than galaxies, gravity pulls matter together to form a web of filaments surrounding nearly empty voids. Galaxies form along the filaments and accumulate in clusters where the filaments intersect.
processes in galaxy formation - galaxy collapse
As a galaxy-size cloud of matter collapses, stars form within in. The stars and interstellar material in a galaxy settle into orbits around a common center. These orbital motions determine the overall shape of the galaxy.
processes in galaxy formation - rotation
As a galaxy contracts, it rotates faster and faster, like a spinning ice skater who pulls in her limbs. Rotation counteracts gravity along a plane, allowing collisions within the gas to produce a disk-shaped spiral galaxy.
processes in galaxy formation - stellar evolution
As stars evolve they can reshape the gas in the galaxy.
processes in galaxy formation - merging
Galaxies can collide and merge to form a more massive galaxy. Probably all large galaxies grow by consuming smaller ones. Elliptical galaxies show evidence of being formed by mergers of large galaxies.