Supermassive black holes in binaries and their accretion discs… Spins align on some timescale, but migration also takes place. Do gas discs have enough time to align the spins? Well, the secret is the mass ratio: light secondaries might prevent primaries from aligning. A great collaboration between gravitational-wave and planet researchers!

Davide Gerosa, Benedetta Veronesi, Giuseppe Lodato, Giovanni Rosotti.
Monthly Notices of the Royal Astronomical Society 451 (2015) 3941-3954.
arXiv:1503.06807 [astro-ph.GA].