LIGO can measure spins. Well, effective spins actually. These are special combinations of the two spins (magnitude and direction) and the binary mass ratio. There’s a ton of astrophysics that can be done just with this quantity, but one should always be careful. Today’s paper points out a few important shortcomings when dealing with effective spin measurements. Want to know more about asymmetries and selection biases?
ps. You can hardly find a better day to post a paper on the arxiv than May 4th