In 2015, the LIGO observatories in Hanford and Livingston detected gravitational waves for the first time, confirming a century-old prediction of general relativity. The signal, labeled GW150914, came from two black holes colliding roughly a billion light-years away. That breakthrough opened an entirely new way to observe the universe. Since then, scientists have been watching the sky for more such events, and evidence is mounting that what they're seeing now are black hole mergers of a different kind: second-generation collisions, where at least one of the black holes involved was itself born from an earlier merger. This matters because it suggests black holes can pile up and combine repeatedly, creating heavier and heavier objects. The waveforms match what physicists predicted these secondary mergers would look like, adding another layer of confirmation to our understanding of gravity itself.