Continuing on with our discussion of the outstanding result of the discovery of gravitational waves, it is interesting to think that this is also the first time a binary black hole has been identified.
This discovery in and of itself is a fascinating one. The only way we know for sure that a black hole can form is by the explosion of a massive star, or supernova. In turn, stars massive enough to go supernova are rather rare, one in a hundred or less.
Here we have the remarkable case of two massive stars forming close to each other, possibly as siblings bound to each other in a binary system from birth. This is already exceedingly rare. Add to this the explosion of each star as a supernova, which is a violent event. Each supernova would be capable of upsetting its twin, causing ejection of the second object from the binary system.
Instead, we have the case of two supernovae events, one for each member of the binary, and the astounding result that neither one manages to blow the system apart completely. Finally, consider that both black holes end up continuing to orbit around their common center of mass just as they did in their youth.
They spin, and lose energy, and get closer and closer to each other until they get close enough to suddenly inspiral and collide with each other. This is the type of merging black hole system that we discovered with the gravitational wave detection announced two weeks ago.
Somewhat surprisingly, we discovered this merging black hold outside the Milky Way first, despite the 100 billion stars in the Milky Way and the large numbers of expected free-floating stellar-mass black holes to choose from. Was this pure luck? Will we also find merging black holes in the Milky Way? Are merging black holes more common that we thought, and if so, will this uncover significant gaps in our astronomical knowledge? Your thoughts and ideas are welcome. Back to it!