 At 9, 50, and 45 seconds, coordinated universal time, on the 14th of September 2015, a signal was detected by the LIGO detector in Livingston and 6.9 milliseconds later in Hanford. It was a chirp signal that lasted just over two-tenths of a second. When we route the wave into a sound generator, here's what it sounds like. This plot combines the data from both sites. The waveform is consistent with coalescing masses, with a 10-cycle 200 millisecond in spiral that gives us the frequency, the rate of change of the frequency, and a peak wave amplitude. A merger that takes around two milliseconds, and a ring down as the coalesced objects cease to radiate gravitational energy. Detector noise introduces errors into all the calculations based on these figures. That's why we'll provide a range for each item. The amplitude and frequency data points give us the luminosity distance. It is important to note that gravitational waves experience redshifting as they travel across the cosmos, just like light does. Having traveled around a billion light years, this wave would have experienced a redshift near 0.1. So the frequency we see here is a bit smaller than the frequency at the start of the wave's journey here. The frequency data also gives us the chirp mass. Taking the redshift information gleamed from the merger and ring down portions of the waveform, we get the binary system masses. These masses are too large for neutron stars that are only a few times the mass of the sun. So we must be witnessing the merger of two large stellar black holes. During the last 200 milliseconds of their in spiral, the orbiting velocity of the black holes increased from 30% the speed of light to 60% of the speed of light. Over the same period, the distance between the two black holes went from around a thousand kilometers to just under 200 kilometers when their event horizons made contact. Modeling the final ring down shows that the mass of the resulting curve black hole is around 62 solar masses. That's three solar masses less than the sum of the masses of the two inspiring black holes. This mass was converted to the radiated gravitational energy. In other words, during the final 20 milliseconds of the merger, the power of the radiated gravitational waves peaked at about 3.6 times 10 to the 49th watts. Let's take a second to get a feel for how large this number is. In our How Far Away Is It segment on nearby stars, we found that the sun converts 4.26 metric tons of matter into energy every second. The resulting power output is equal to 4 billion hydrogen bombs exploding every second. The sun is an average star, so we can use this as an average stellar power output. From our segment on local superclusters, we saw that there are 250,000 trillion stars within 1 billion light years. This represented around 7% of the total number of stars in the universe. We get the total power emitted by all the stars in the visible universe by multiplying the average watts per star times the number of stars. The power generated by this merger of the two stellar mass black holes is 26,000 times greater than the combined power of all the light radiated by all the stars in the universe. That's the signal we saw in September 2015, a billion years after it happened.