The Milky Way is ‘rippling’ like a pond, and scientists may finally know why

Think of the 100 billion stars of the Milky Way as a flat, calm pool of water. Now imagine if someone dropped a rock the size of 400 million suns into that water. The calm is shaken. Wave after wave of energy ripples across the galaxy’s surface, jostling and bobbing its stars in a chaotic dance that takes eons to settle.

Astronomers suspect that something like this could really have happened — not just once, but several times over the past billions of years.