Gravitational wave strain h(t)
Frequency-time spectrogram (chirp)
First detected by LIGO on September 14, 2015, GW150914 confirmed Einstein's 100-year-old prediction: merging black holes distort spacetime itself at a strain of h ~ 10⁻²¹ — squeezing a 4 km arm by a proton's width. The characteristic chirp signal rises in frequency and amplitude as the inspiral tightens, then cuts off at merger into a ringdown. Energy radiated: ~3 solar masses converted to gravitational waves in 0.2 seconds — briefly outshining all stars in the observable universe combined.