While black holes don’t emit light, the material falling toward their event horizon will form a disk that can grow in size until it is dense enough to ignite with nuclear reactions. These disks in actively feeding galaxies and the innermost stars in starving systems like our Milky Way’s Sgr A* let us measure the speeds of objects near the event horizon of the black hole, and those speeds are influenced by the rate the black hole itself is spinning. This is because a spinning black hole can literally drag space-time around with it.

In new observations of the quasar H1821+643, researchers have discovered this actively spinning system is rotating more slowly than expected. At thirty billion solar masses, this is a massive system that dwarfs our galaxy’s four million solar mass black hole. And while our black hole rotates at a pace that isn’t too different from other similarly sized behemoths, this supersized supermassive black hole is lumbering around at a much slower rate. This difference is consistent with supermassive black holes growing over time through the merger of small galaxies and their smaller supermassive black holes. Since these mergers happen from all sorts of different directions and angles, they will typically slow the rotation of the black hole as systems chaotically merge.

Conveniently, this matches theory, and science appears to be marching on with one really big thing making sense.

More Information

CXO press release

CXO photo release

“Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole in the cluster-hosted quasar H1821+643,” Júlia Sisk-Reynés, Christopher S. Reynolds, James H. Matthews, and Robyn N. Smith, accepted to Monthly Notices of the Royal Astronomical Society (preprint)