Monster black hole merger is biggest ever seen

The biggest ever merger of colliding black holes involved holes that were too massive to have formed from collapsing stars. And the holes were spinning about 40 times per second — near the limit of what Einstein’s general theory of relativity allows. These ‘forbidden’ high-mass black holes might have been the product of an earlier merger. It’s like “four grandparents merging into two parents merging into one baby black hole”, says physicist Alan Weinstein.