Investigating Optical and Ring-Down Gravitational Wave Properties of a Rotating Black Hole in a Dehnen Galactic Dark Matter Halo

TL;DR

This study models a rotating black hole within a Dehnen dark matter halo, analyzing how halo properties influence horizon structure, shadows, and ringdown signals, thus aiding in dark matter detection via gravitational and optical observations.

Contribution

We extend the Kerr solution to include a Dehnen dark matter halo, revealing its impact on black hole properties and observable signals, which is a novel approach in black hole-dark matter interaction studies.

Findings

Halo parameters significantly affect black hole shadow shape and size.

Dark matter halo alters horizon and ergoregion dimensions.

Ringdown frequencies are highly sensitive to halo profiles.

Abstract

We present a comprehensive study of the optical and dynamical properties of a rotating black hole immersed in a Dehnen-type $(1,4,0)$ galactic dark matter halo, modeled by a double power-law density profile commonly used to describe realistic galactic cores. By extending our previous Schwarzschild-Dehnen solution using a modified Newman-Janis algorithm, we construct a Kerr-like axisymmetric spacetime that smoothly incorporates both black hole rotation and the influence of the surrounding dark matter halo. We systematically investigate the effects of the halo parameters-the central density and halo radius-on horizon structure, the shape and extent of the ergoregion, and the null geodesics associated with black hole shadows. Our results show that the presence of a dense or extended halo expands the event horizon and ergoregion, and significantly alters the size and distortion of the black hole shadow. Furthermore, by applying the WKB approximation to scalar field perturbations, we compute the quasinormal mode (QNM) spectra and demonstrate that the frequencies and damping times of ringdown signals are highly sensitive to the halo profile. These results open promising avenues for probing the dark matter environment of astrophysical black holes through black hole imaging and gravitational wave observations.