Spiral Arms

This site tells the story of the history of the universe. Click Earlier and Later to follow the story.
Note: Many facts have been simplified to make them easier to understand.
Our new free weekly podcast Time Crystal tells this story as sci-fi fantasy

Looking from above the disc of a spiral galaxy like the Milky Way a new picture appears. We can see dense spiral arms in the disc of the Galaxy. We think it is gravity which created the spiral pattern, although the details are not clear. The spiral arms are places where the gas of the disc is squashed together.
Note that we have never actually seen our own Galaxy from the outside. The picture shown here is of another spiral galaxy, but we think ours is similar!
New and important stars form these spiral arms.