http://arxiv.org/abs/2210.09357
Circumambient and galactic-scale environments are intermittently present around black holes, especially those residing in active galactic nuclei. As supermassive black holes impart energy on their host galaxy, so the galactic environment affects the geodesic dynamics of solar-mass objects around supermassive black holes and subsequently the gravitational waves emitted from such non-vacuum extreme-mass-ratio binaries. Only recently an exact general-relativistic solution has been found that describes a Schwarzschild black hole immersed in a dark matter halo profile of the Hernquist type. We perform an extensive geodesic analysis of test particles delving in such non-vacuum spacetimes and compare our results with those obtained in vacuum Schwarzschild spacetime, as well as their dominant gravitational-wave emission. Our findings indicate that the radial and polar oscillation frequency ratios, which indicate resonances, descend deeper into the extreme gravity regime as the compactness of the halo increases. This translates to a gravitational redshift of non-vacuum geodesics and their resulting waveforms with respect to the vacuum ones; a phenomenon which has also been observed for ringdown signals in these setups. For compact environments, we find that the apsidal precession of orbits is strongly affected due to the gravitational pull of dark matter; the orbit’s axis can rotate in the opposite direction as that of the orbital motion, leading to a retrograde precession drift that depends on the halo’s mass, as opposed to the typical prograde precession transpiring in vacuum and galactic-scale environments. Gravitational waves in retrograde-to-prograde orbital alterations demonstrate transient frequency phenomena around a critical non-precessing turning point, thus they may serve as a `smoking gun’ for the presence of dense dark matter environments around supermassive black holes.
K. Destounis, A. Kulathingal, K. Kokkotas, et. al.
Wed, 19 Oct 22
28/87
Comments: 14 pages, 7 figures