Binary systems radiate out gravitational waves. Google image search for "binary system gravitational waves" and you will pretty easily identify the canonical gr

Binary systems radiate out gravitational waves. Google image search for "binary system gravitational waves" and you will pretty easily identify the canonical graphical representation. While there are lots of problems with the "sheet" analogy for general relativity, there is still value in considering gravitational radiation to be waves in the sheet. From a layman perspective, the analogy is irresistible. The mental picture of the spiraling-in process is pretty easy to grasp, but the process of gravitational capture is a little more difficult. Gravitational radiation is extremely dependent on the distance of the mutual orbit, so the inward spiral progresses rapidly at short distances, but can take a very long time at greater distances. So I imagine the research comes down to the general statistics of the formation of binary systems, how often they will involve a neutron star with a black hole, and how often they form at distances close enough to create the collision.