Not only do galaxies spin, the Milky Way is whipping our solar system around at 514,000 mph (828,000 km/h). Yet it's so incredibly vast that the sun has only made 20 orbits since it formed.
Even at that blistering speed, it takes our solar system roughly 225 to 250 million years to complete a single trip—a duration known as a galactic year. This spinning motion is one of the most defining physical characteristics of galaxies across the universe, and it is a leftover consequence of how they first formed. In the early universe, galaxies began as massive clouds of hydrogen and helium gas. As gravity caused these clouds to collapse inward, any slight initial rotation they possessed was amplified. Just as a spinning figure skater accelerates by pulling their arms in toward their body, the collapsing gas cloud spun faster due to the conservation of angular momentum. This centrifugal force caused the gas to flatten out into a disk, creating the classic shape seen in spiral galaxies.
Not all galaxies spin in such an orderly fashion. While spiral galaxies rotate as cohesive disks, elliptical galaxies are shaped more like footballs or spheres. Their stars still move and possess angular momentum, but they travel in chaotic, disorganized orbits rather than moving together in a single plane. Think of an elliptical galaxy less like a spinning record and more like a swarming hive of bees.
The way galaxies spin also provided astrophysicists with the first major evidence for dark matter. According to Newtonian physics, stars at the outer edges of a spiral galaxy should orbit slower than those near the dense, massive center—just as Pluto orbits the sun much slower than Mercury. Instead, observations in the 1970s revealed that galaxies rotate at a relatively constant speed all the way out to their edges. The only way this flat rotation curve is physically possible without the galaxy flying apart is if it is embedded in a massive, invisible halo of dark matter whose gravitational pull holds the spinning stars together.