Merging Compact Binaries in Hierarchical Triple Systems: Resonant Excitation of Binary Eccentricity

摘要

We study the secular dynamics of compact binaries (consisting of whitedwarfs, neutron stars or black holes) with tertiary companions in hierarchicaltriple systems. As the inner binary (with initially negligible eccentricity)undergoes orbital decay due to gravitational radiation, its eccentricity can beexcited by gravitational forcing from the tertiary. This excitation occurs whenthe triple system passes through an "apsidal precession resonance", when theprecession rate of the inner binary, driven by the gravitational perturbationof the external companion and general relativity, matches the precession rateof the outer binary. The eccentricity excitation requires the outer companionto be on an eccentric orbit, with the mutual inclination between the inner andouter orbits less than $\sim 40^\circ$. Gravitational wave (GW) signals fromthe inner binary can be significantly modified as the system evolves throughthe apsidal precession resonance. For some system parameters (e.g., a whitedwarf binary with a brown dwarf tertiary), the resonance can happen when thebinary emits GWs in the $10^{-4}-10^{-1}$~Hz range (the sensitivity band ofLISA).