More than seven billion years ago, two immense black holes circled each other until they collided and merged, a cataclysm so intense that it sent ripples soaring through the fabric of space-time. In the early morning hours of May 21, 2019, Earth trembled from the vibrations sent off by this distant carnage, cluing in astronomers to the biggest cosmic bang they’d ever detected—and one that defies theoretical expectation.

MG