No evidence that the majority of black holes in binaries have zero spin

Understand

The spin properties of merging black holes observed with gravitational waves can offer novel information about the origin of these systems.

• The magnitude and orientations of black hole spins offer a record of binaries' evolutionary history, encoding information about massive stellar evolution and the astrophysical environments in which binary black holes are assembled.
• Recent analyses of the binary black hole population have yielded conflicting portraits of the black hole spin distribution.
• Some work suggests that black hole spins are small but non-zero and exhibit a wide range of misalignment angles relative to binaries' orbital angular momenta.