Kavli Affiliate: Pau Amaro Seoane
| First 5 Authors: Alessandra Mastrobuono-Battisti, Pau Amaro Seoane, Màrius Josep Fullana i Alfonso, Chingis Omarov, Denis Yurin
| Summary:
We address the orbital distribution of stars in merging nuclear star clusters
(NSCs) and the subsequent effects on supermassive black hole binary (SMBHB)
evolution. We ran direct-summation $N$-body simulations with different initial
conditions to do a detailed study of the resulting NSC after their progenitors
had merged. Our findings reveal that prograde stars form a flattened structure,
while retrograde stars have a more spherical distribution. The axial ratios of
the prograde component vary based on the presence and mass ratio of the SMBHs.
The fraction of prograde and retrograde stars depends on the merger orbital
properties and the SMBH mass ratio. The interactions of retrograde stars with
the SMBHB affect the eccentricity and separation evolution of the binary. Our
analysis reveals a strong correlation between the angular momentum and
eccentricity of the SMBH binary. This relationship could serve as a means to
infer information about the stellar dynamics surrounding the binary. We find
that prograde orbits are particularly close to the binary of SMBHs, a promising
fact regarding extreme mass ratio inspiral (EMRI) production. Moreover,
prograde and retrograde stars have different kinematic structures, with the
prograde stars typically rotating faster than the retrograde ones. The
line-of-sight velocity and velocity dispersion, as well as the velocity
anisotropy of each NSC, depend on the initial merger orbital properties and
SMBH mass ratios. The prograde and retrograde stars always show different
behaviours. The distribution of stellar orbits and the dynamical properties of
each kinematic population can potentially be used as a way to tell the
properties of the parent nuclei apart, and has an important impact on expected
rates of EMRIs, which will be detected by future gravitational wave
observatories such as the Laser Interferometer Space Antenna (LISA). [abridged]
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