Looks like some of the LIGO black holes have low spins (better, low effective spins). In this paper we show these values can be accommodated with standard “field binaries”, i.e. formation channels where binary black holes form from binary stars.

Krzysztof Belczynski, Jakub Klencki, Carl E. Fields, Aleksandra Olejak, Emanuele Berti, Georges Meynet, Christopher L. Fryer, Daniel E. Holz, Richard O’Shaughnessy, Duncan A. Brown, Tomasz Bulik, Sching C. Leung, Ken’ichi Nomoto, Piero Madau, Raphael Hirschi, Etienne Kaiser, Samuel Jones, Samaresh Mondal, Martyna Chruslinska, Paweł Drozda, Davide Gerosa, Zoheyr Doctor, Mirek Giersz, Sylvia Ekström, Cyril Georgy, Abbas Askar, Vishal Baibhav, Daniel Wysocki, T. Natan, Will M. Farr, Grzegorz Wiktorowicz, M. Coleman Miller, Ben Farr, Jean-Pierre Lasota.
Astronomy & Astrophysics, in press.
arXiv:1706.07053 [astro-ph.HE].