How Scientists Finally Weighed a Black Hole’s Most Violent Outburst

For eighteen years, radio telescopes have been staring at the same small patch of sky in the constellation Cygnus, watching a black hole do something that black holes do rather well: devour its companion star and fling what it can’t swallow back into the universe at half the speed of light. The watching has been patient, meticulous, and until very recently, frustrating. The jets blazing outward from the black hole known as Cygnus X-1 were obviously powerful. How powerful, exactly, remained...