Particle Motion in Regular Black Hole Spacetimes Supported by a Galactic Halo

TL;DR

This work investigates how a Dehnen-type galactic halo modifies strong-field signatures of regular, asymptotically flat black holes. By analyzing two analytic halo-supported metrics with halo scale a, the authors compute circular and null geodesics, photon-sphere properties, shadow radii, Lyapunov exponents, ISCO frequencies, binding energies, and Hawking temperatures, highlighting the halo's impact on observables. They find that increasing a generally shrinks horizon and photon-sphere radii while enhancing orbital instability and accretion efficiency for moderate density slopes (γ ≈ 3.5–4); for γ = 5, deviations from Schwarzschild are minimal, indicating a sensitivity to the asymptotic density falloff. The results underscore that environmental halo effects can affect optical and dynamical black hole signatures, with the magnitude of modifications governed by both the halo scale and density profile.

Abstract

We investigate particle motion in regular and asymptotically flat black hole spacetimes supported by Dehnen-type dark-matter halos. Two analytic models are analyzed, allowing a systematic study of circular geodesics, photon-sphere properties, shadow radius, Lyapunov exponent, ISCO frequency, binding energy, and Hawking temperature. The corrected numerical results show that the halo scale parameter can significantly modify strong-field observables. In both models, for moderate density slopes, increasing the halo parameter reduces characteristic radii while enhancing orbital instability and accretion efficiency. For steeper density falloff, however, deviations from the Schwarzschild case remain small. These results demonstrate that halo-induced modifications of optical and dynamical black hole signatures are strongly controlled by the density profile parameters.