I was watching this video by Veritasium (note: I don't have much physics knowledge). As I understand, at LIGO they detect the gravitational waves that were generated by the collision of the two black holes. How can they still measure these waves if the energy that they measure was released was only the last 10th of the seconds of the merging black holes (as I understand from the video)? As far as I understand, that would mean that there is only one peak that they can measure, which is that 10th of a second, but their experiment seems to be going on many years and they have made many measurements. How is this possible if the final collision was so short? What do they really measure then?
Basically my question comes down to: was that a "once in a lifetime chance" of measuring the waves? Have they been sitting there waiting for the exact moment and then do a measurement? It isn't something they can measure everyday?