Astronomy, Public, Pythagorean Astronomy, Radio and Podcasts

Pythagorean Astronomy: Black holes – too big and too small

Chris North

3 September 2020

Artist’s impression of two black holes about to collide. Image credit: Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav).

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 are 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’s a lecturer at the University of Birmingham.

We also come across black holes in the hearts of galaxies, and it’s 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’t so super. Dr Federico Lelli, from Cardiff University explains all, from what a supermassive black hole is, to why this one is so interesting.

An extended edition of an original broadcast on 3rd September 2020 as part of Pythagoras’ Trousers on Radio Cardiff.