Partial suppression of chaos in relativistic three-body problems

Abstract

Recent numerical results seem to suggest that in certain regimes of typical particle velocities the gravitational $N-$body problem (for $3\leq N\lesssim 10^3$) is intrinsically less chaotic when the post-Newtonian (PN) force terms are included, with respect to its classical counterpart that exhibits a slightly larger maximal Lyapunov exponent $\Lambda_{\rm max}$. In this work we explore the dynamics of wildly chaotic, regular and nearly regular configurations of the 3-body problem with and without the PN corrective terms aiming at shedding some light on the behaviour of the Lyapunov spectra under the effect of said corrections. Because the interaction of the tangent-space dynamics in gravitating systems, needed to evaluate the Lyapunov exponents, becomes rapidly computationally heavy due to the complexity of the higher order force derivatives involving multiple powers of $v/c$, we introduce a technique to compute a proxy of the Lyapunov spectrum based on the time-dependent diagonalization of the inertia tensor of a cluster of trajectories in phase-space. We find that, for a broad range of orbital configurations, the relativistic 3-body problem has a smaller $\Lambda_{\rm max}$ than its classical counterpart starting with the exact same initial condition. However, the rest of the Lyapunov spectrum can be either lower or larger in the classical case, suggesting that the relativistic precession effectively reduces chaos only along one (or few) directions in phase-space. As a general trend, the dynamical entropy of the relativistic simulations as function of the rescaled speed of light always has a regime in which falls below the classical value.} We observe that, the sole analysis of $\Lambda_{\rm max}$ could induce possibly misleading conclusions on the chaoticity of systems with small (and possibly large $N$.