Their gravitational battle was short-lived, however. In a fraction of a second, the two rapidly spinning objects touched and unleashed a fury of energy. In an instant, the black holes lost 3 times the mass of our sun - this mass was converted into pure gravitational energy, peaking in power output 50 times the output of all the stars in the universe combined.
If we remember our "tossing a pebble in a pond" analogy for the generation of gravitational waves, this black hole merger was like throwing a brick into that pond; a gargantuan surge of gravitational wave energy erupted, blasting these spacetime ripples into the universe.
ANALYSIS: More Gravitational Wave Rumors: Colliding Black Holes?
Then, 1.3 billion years later, these waves reached Earth. And it just so happened that LIGO had only just been upgraded to detect this ancient event. It's cosmic serendipity at its finest.
Theory suggests that when two black holes collide and merge, their gravitational wave signal should produce a very fast pulse and, if slowed down sufficiently, the rapid spinning and collision should be represented in the waves as a "chirp." And guess what? Almost exactly as predicted by computer models based on Einstein's 100-year-old equations of general relativity, the black hole merger "chirped." Listen: