Billions of years ago, one, relatively small galaxy cluster ran by the Perseus galaxy cluster, one of the largest objects in the known universe, which measures 11 million light years across. When that smaller cluster clipped Perseus, it set of a sequence that created a giant wave of gas, NASA scientists think.
The gravitational bump agitated Perseus’ gas, “like cream stirred into coffee,” as NASA puts it, and started a spiral of gas that after 2.5 billion years, formed waves that rolled out of the Perseus cluster, just like waves on the ocean.
The wave, which is simulated in the video above, is thought to be 200,000 light years across, which is two times the size of our own vast galaxy, the Milky Way. It’s enough to make a person feel small—and a little less guilty about bumping into another human on the street. At least people-to-people collisions don’t create effects that last billions of years.