Relaxation near supermassive black holes driven by nuclear spiral arms:
  anisotropic hypervelocity stars, S-stars and tidal disruption events
  Nuclear spiral arms are small-scale transient spiral structures found in the
centers of galaxies. Similarly to their galactic-scale counterparts, nuclear
spiral arms can perturb the orbits of stars. In the case of the Galactic Center
(GC), these perturbations can affect the orbits of stars and binaries in a
region extending to several hundred parsecs around the supermassive black hole
(MBH), causing diffusion in orbital energy and angular momentum. This diffusion
process can drive stars and binaries to close approaches with the MBH,
disrupting single stars in tidal disruption events (TDEs), or disrupting
binaries, leaving a star tightly bound to the MBH, and an unbound star escaping
the galaxy, i.e., a hypervelocity star (HVS). Here, we consider diffusion by
nuclear spiral arms in galactic nuclei, specifying to the Milky Way GC. We
determine nuclear spiral arm-driven diffusion rates using test-particle
integrations, and compute disruption rates. Our TDE rates are up to 20% higher
compared to relaxation by single stars. For binaries, the enhancement is up to
a factor of ~100, and our rates are comparable to the observed numbers of HVSs
and S-stars. Our scenario is complementary to relaxation driven by massive
perturbers. In addition, our rates depend on the inclination of the binary with
respect to the Galactic plane. Therefore, our scenario provides a novel
potential source for the observed anisotropic distribution of HVSs. Nuclear
spiral arms may also be important for accelerating the coalescence of binary
MBHs, and for supplying nuclear star clusters with stars and gas.
