Pythagorean Astronomy

If there’s anything that pricks up the ears in astronomy, it’s black holes. And this month we have not one, but two black hole stories. And, depending on how you count them, four black holes, though two of them no longer exist – if that sounds confusing, then don’t worry, it’ll become clear! Regular listeners will be no stranger to black holes, with them featuring regularly – largely thanks to the work of the LIGO and Virgo gravitational wave experiments, which detect the subtle ripples in the fabric of spacetime as pairs of black holes merge. Those black holes are thought to be the remnants of dead stars, and are typically called “stellar mass” black holes since their masses are typically between a few and a few tens of times the mass of our Sun. The detection we’re talking about this month comes from the third observing run, and is the latest in a string of announcements as the long list of candidate events have been studied in further detail and released. Called GW190521 it was observed in May 2019, and