The detectors have sensed dozens of such cataclysms over the past 5 years, but the one on 21 May 2019 was different. Not only was it the most powerful and distant merger ever seen, but the resulting black hole also belongs to a class of long-sought middleweight black holes, members of the LIGO-Virgo collaboration report today in two new studies. Puzzlingly, however, the two black holes that merged are heavier than expected: Their masses fall in a gap in which theorists … See More.