Gravitational waves are ripples in the fabric of spacetime caused by cataclysmic events such as neutron stars colliding and black holes merging.
The biggest of these events, and the easiest to see, are the collisions between supermassive black holes at the centre of galaxies. So an important question is how often these events occur.
Today, Sean McWilliams and a couple of pals at Princeton University say that astrophysicists have severely underestimated the frequency of these upheavals. Their calculations suggest that galaxy mergers are an order of magnitude more frequent than had been thought.