h31

After the special h “discovery issue” announcing and celebrating the first detected gravitational wave event, we go on with a “normal” issue, announcing a not-less outstanding achievement: the detection of two other events confirming clearly the detection of gravitational waves and the existence of black holes of a large mass range.
In the Virgo community there is some modesty/reticence in speaking of two new events, since one of them provides a quite weak signal. I don’t share this attitude: one has simply to quote the statistical significance of each event, the weak one being a “two sigma” event, while the strong ones are of a “five sigma” quality. In other words, we can say that the corresponding probability of having false events of the same amplitude is, respectively, one event every few years and one event every few million years!

C.Bradaschia
Chief Editor