Soon after the two advanced LIGO detectors were ready in September 2015 for a calibrated observation run, a giant gravitational wave burst hit the detectors and were duly recorded as nearly identical chirped signal wave spiralling up in frequency and amplitude from 35 to 250 Hz, with a relative delay of 6.9 ms, well inside the light travel distance of 10 ms between the two detectors. The peak strain amplitude touched 100 times the base sensitivity. Analysis of the 200 ms short event led to the robust conclusion that LIGO detectors saw gravitational waves from two orbiting and merging black holes of nearly 30 solar mass each, at a distance of about 1.3 billion light years. We sketch this double discovery of great scientific and astronomical importance - the terrestrial detection of gravitational waves, ushering in the era of gravitational wave astronomy, and the discovery of a stellar mass binary black hole system, observed during their orbital evolution towards merger and then to the formation of a single stable black hole, all invisible to any other form of astronomy.
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