Formation of counter-rotating and highly eccentric massive black hole binaries in galaxy mergers

ABSTRACT Supermassive black hole (SMBH) binaries represent the main target for missions such as Laser Interferometer Space Antenna and Pulsar Timing Arrays. The understanding of their dynamical evolution prior to coalescence is therefore crucial improving detection strategies astrophysical interpretation gravitational wave data. In this paper, we use high-resolution N-body simulations model merger two equal-mass galaxies hosting a central SMBH. our models, all are initially prograde with respect galaxy sense rotation. But, that form high eccentricity, e ≳ 0.7, quickly reverse rotation become almost perfectly retrograde at moment binary formation. these proceeds towards larger eccentricities, expected hardening in counter-rotating stellar distribution. Binaries lower eccentricities remain comparatively low eccentricities. We study origin orbital flip by using an analytical describes early stages evolution. This indicates plane due torque from triaxial background mass distribution naturally arises galactic process. Our results imply existence population SMBH eccentricity could have significant implications signal emitted systems.