&gt; Was that extremely coincidental? Or do these events happen all the time, and so if it wasn&#x27;t those two black holes it would be two others?<p>From the article, no one knows: &quot;Black holes, the even-more-extreme remains of dead stars, could be expected to do the same, but nobody knew if they existed in pairs or how often they might collide. If they did, however, the waves from the collision would be far louder and lower pitched than those from neutron stars.&quot;