Gravitational-wave data keep on giving us surprises. The most outstanding one IMO is an observed correlation between mass ratios and spins of the black holes, which was first found by Tom Callister and friends. That is so, so weird… to the point that virtually zero astrophysical models so far can explain it fully and consistently. Well, we can’t either (at least not fully and consistently) but we think this paper is a nice attempt. The secret seems to be the symmetry of the astrophysical environment one considers, and data tends to prefer black holes assembled in cylindrical symmetry. That’s also weird to be honest, but there’s a candidate for this setup, namely accretion disks and their migration traps. Who knows, more data will tell.

… and huge congrats to my MSc student Alessandro who managed to publish a paper even before graduating!

Alessandro Santini, Davide Gerosa, Roberto Cotesta, Emanuele Berti
arXiv:2308.12998 [astro-ph.HE].
Physical Review D 108 (2023) 083033.
Other press coverage: astrobites.