Regarding "GW150914", the gravitational wave event detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14, 2015, which of the following statements are true? Select each true answer (there may be several)
A. The gravitational waves were emitted during the final 0. 2 seconds of the orbital inspiral and merger of two massive black holes in the distant universe.
B. This event represents the first direct detection of gravitational waves in human history, and for this reason, prompted award of the 2017 Nobel Prize in Physics to LIGO.
C. The properties of the signal, in particular the "ringdown" portion, can be considered the first proof of the existence of black holes (event horizons) in our universe.