Not really funny....Most systems are binary, trinary or even larger. http://hyperphysics.phy-astr.gsu.edu/hbase/astro/blkbin.html https://en.wikipedia.org/wiki/Binary_system And even if one or both remnants were Neutron stars, they can in time turn into BH's. And of course the two BH's straying together is another possibility. The point is it happened, and we have more 'chirps" yet to investigate or in the process of investigation. Wonderful news all round!