Gerosa1

Binary black holes spiral in very slowly through the emission of gravitational radiation; most mergers should occur millions to billions of years after the binary’s birth. During this slow inspiral, coupling between angular momenta has been thought to scramble their relative orientations. That’s unfortunate: the spin and orbit orientations at birth reflect the processes that formed the binary, notably supernova, which misalign the spin and orbital plane.

In Gerosa et al (2013), my collaborators and I suggest that the relative spin orientations are significantly less scrambled than previously assumed. In particular, we suggest the relative spin orientations may encode the birth order, potentially allowing gravitational wave measurements to identify which member of the binary was formed first.

For experts: For relativists, our paper demonstrates post-Newtonian resonances can be populated over a wide range of angles. For astrophysicists, our cartoon model of binary evolution proposes an alternative approach to spin alignment in binary evolution codes: tidal alignment during the Herzprung gap, prior to the common envelope phase.

For more information, see

• Our paper: Gerosa et al 2013, PRD 87 4028