Gerosa2

Previously, my collaborators and I argued (a) that the spin and orbit orientations at birth reflect the processes that formed the binary, notably supernova, which misalign the spin and orbital plane; and (b) that some information about these orientations was preserved as the binary spiralled inwards for millions to billions of years until merger. Specifically, we claimed the relative spin orientations at merger may encode the birth order.

In a recent study, varying a limited set of parameters, we argue that the two resonant families seem to produce distinguishable gravitational waves.
In other words, gravitational wave measurements might be able to identify which member of the binary was formed first.

We haven’t performed an exhaustive study (“parameter estimation”); followup work is underway. But our results are a promising beginning.

For experts : For relativists, our paper uses two arguments to suggest that members of the twin resonant families can be distinguished using their gravitational waves. First, we argue based on dynamics: one resonance has both spins on the same side of J as the orbital angular momentum; the other has both spins opposite one another. In the first case, the orbital plane precesses little. In the second, it precesses a lot.
Second, using a pessimistic choice of viewing direction (along J) for both source and template, minimizing precession-induced modulations, we calculate a fitting factor that is significantly different from unity.

For more information, see

• Gerosa et al, Capulets and Montagues: distinguishing the rival families of black-hole spin-orbit resonances by their gravitational-wave signatures arxiv.org:1403.7147

• Our prior work, arguing the two populations remain distinct : Gerosa et al 2013, PRD 87 4028