“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae.” -Scott Adams
Everyone knows the recipe for a black hole: create a massive enough star, allow it to burn through the fuel it its core, and wait. After enough time, the core will collapse, creating a type II supernova and a runaway fusion reaction. The outer layers explode while the core implodes, leaving behind a black hole if it’s massive enough. Alternatively, merge two failed black holes — i.e., neutron stars — together, and you get a black hole, too.
Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. About 3-5% of the mass gets expelled in such a collision; the rest becomes a single black hole. Image credit: Dana Berry, SkyWorks Digital, Inc.
But there ought to be a third way: through direct collapse. We haven’t seen enough supernovae for the stars that exist, and we don’t have a great explanation, otherwise, for ...