Lots of “firsts” today! My first-year PhD student Viola just put out her first first-author paper. This is about measuring black holes with not one, but two precessing spins. People have been trying to figure out how to tell if at least one of the two spins of a merging black-hole binary is precessing for quite some time now. And maybe we’ve even done it already for one or two of the current LIGO-Virgo events. But here I must quote that epic Italian commercial from the 90s: “two gust is megl che one” (which is a terrible Italian-English mishmash on a terrible joke to say that when you eat a Maxibon “two flavors are better than one”). In this paper we propose a strategy to identify sources that have the strongest evidence of two processing spins. Viola has been putting together simulated data for the next LIGO/Virgo data-taking period, and the result is pretty cool. If these binaries are out there in the Universe, we will be able to tell they have two spins going around!

Viola De Renzis, Davide Gerosa, Geraint Pratten, Patricia Schmidt, Matthew Mould.
Physical Review D 106 (2022) 084040.
arXiv:2207.00030 [gr-qc].