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If there\u2019s anything that pricks up the ears in astronomy, it\u2019s 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 \u2013 if that sounds confusing, then don\u2019t worry, it\u2019ll become clear!\n\nRegular listeners will be no stranger to black holes, with them featuring regularly \u2013 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 \u201cstellar mass\u201d black holes since their masses are typically between a few and a few tens of times the mass of our Sun.\n\nThe detection we\u2019re 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 immediately caused a stir among the researchers. To find out why, we're joined by Dr Patricia Schmidt. Patricia was a PhD student here in Cardiff a few years ago, and after working the US and the Netherlands is now back in the UK, where she\u2019s a lecturer at the University of Birmingham.\n\nWe also come across black holes in the hearts of galaxies, and it\u2019s thought that all large galaxies harbour a so-called supermassive black hole at their core, typically measuring millions or even billions of times the mass of the Sun. A recent study measured the mass of one of these supermassive black holes and found that it, well, isn\u2019t so super. Dr Federico Lelli, from Cardiff University explains all, from what a supermassive black hole is, to why this one is so interesting.\n\nAn extended edition of an original broadcast on 3rd September 2020 as part of Pythagoras' Trousers on Radio Cardiff.