When two black holes (BHs) merge, the end state is believed to be a
Kerr black hole, characterized by only its mass, angular momentum,
and linear momentum. All other degrees of freedom, a.k.a. hair, are
radiated away as gravitational waves. From far away, this process
can be viewed as a scattering problem: The initial state is defined
by spins and masses of the two BHs and the final state is defined
by the mass, spin and recoil velocity of the remnant BH.
Modeling the remnant properties of binary black holes is of great
astrophysical interest. It is a crucial element in tests of general
relativity (GR), particularly testing the Kerr hypothesis, no hair
theorem, consistency of GR in predicting the inspiral and ringdown,
and so on. The remnant properties are also important in modeling
the ringdown part of the gravitational wave signal, since the
quasi-normal mode frequencies are entirely determined by the
remnant. Because of the highly dynamical nature of the merger,
prediction of the remnant properties is only possible through
Since numerical simulations are very expensive, several fits have
been developed over the years for the remnant mass, spin and recoil
kick as functions of the component parameters. However, most of
these have only been calibrated against simulations where the
component spins are aligned to the orbital angular momentum. When
the spins are misaligned, they couple with the orbital angular
momentum, and each other and cause the orbital plane to precess.
Therefore, precessing BBH are much harder to model, but they also
have much richer physics!
In this work we construct fits for the remnant properties of
precessing BBH by directly training our model against hundreds
of precessing numerical simulations. We show more than an order
magnitude improvement in the accuracy of predicting remnant
properties. These results are presented in 1809.09125, and our
models are available through a public Python package surfinBH. Also, our paper was
covered by a Caltech press release!
Here's a visualization of the inspiral
and merger of a precessing BBH system. After the BHs merge, you can
see the final remnant BH. At the end, the movie is sped up and you
can see the remnant BH fly away with the recoil velocity.
See: binaryBHexp for more details about this