Theoretical astrophysics and plasma physics at RPC

Abstract:

Since its formulation by Sir Isaac Newton, the problem of solving the equations of motion for three bodies under their own gravitational force has remained practically unsolved. Currently, the solution for a given initialization can only be found by performing laborious iterative calculations that have unpredictable and potentially infinite computational cost, due to the system's chaotic nature. We show that an ensemble of converged solutions for the planar chaotic three-body problem obtained using an arbitrarily precise numerical integrator can be used to train a deep artificial neural network (ANN) that, over a bounded time interval, provides accurate solutions at a fixed computational cost and up to 100 million times faster than the numerical integrator. In addition, we demonstrate the importance of training an ANN using converged solutions from an arbitrary precise integrator, relative to solutions computed by a conventional fixed precision integrator, which can introduce errors in the training data, due to numerical round-off and time discretization, that are learned by the ANN. Our results provide evidence that, for computationally challenging regions of phase space, a trained ANN can replace existing numerical solvers, enabling fast and scalable simulations of many-body systems to shed light on outstanding phenomena such as the formation of black hole binary systems or the origin of the core collapse in dense star clusters.

Abstract:

Although their existence is not yet confirmed observationally, intermediate mass black holes (IMBHs) may play a key role in the dynamics of galactic nuclei. In this paper, we neglect the effect of the nuclear star cluster itself and investigate only how a small reservoir of IMBHs influences the secular dynamics of stellar-mass black hole binaries, using N-body simulations. We show that our simplifications are valid and that the IMBHs significantly enhance binary evaporation by pushing the binaries into the Hill-unstable region of parameter space, where they are separated by the SMBH's tidal field. For binaries in the S-cluster region of the Milky Way, IMBHs drive the binaries to merge in up to 1-6% of cases, assuming five IMBHs within 5 pc of mass 10,000 solar masses each. Observations of binaries in the Galactic center may strongly constrain the population of IMBHs therein.

Abstract:

© 2020 The Author(s). Many astrophysical scenarios have been proposed to explain the several black hole (BH) and neutron star binary mergers observed via gravitational waves (GWs) by the LIGO-Virgo collaboration. Contributions from various channels can be statistically disentangled by mass, spin, eccentricity, and redshift distributions of merging binaries. In this paper,we investigate the signatures of BH-BH binary mergers induced by a third companion through the Lidov-Kozai mechanism in triple systems. We adopt different prescriptions for the supernovae natal kicks and consider different progenitor metallicities and initial orbital parameters. We show that the typical eccentricity in the LIGO band is 0.01-0.1 and that the merger rate is in the range 0.008-9Gpc-3 yr-1, depending on the natal kick prescriptions and progenitor metallicity. Furthermore, we find that the typical distribution of effective projected spin is peaked at Xeff ~ 0 with significant tails. We show that the triple scenario could reproduce the distribution of Xeff. We find that the triple channel may be strongly constrained by the misalignment angle between the binary component spins in future detections with spin precession.