Dehnen halo effect on a black hole in an ultra-faint dwarf galaxy

TL;DR

This study models black holes within ultra-faint dwarf galaxies using Dehnen dark matter profiles, analyzing observable effects like shadows and deflection angles to distinguish between cored and cuspy dark matter distributions.

Contribution

It introduces a rotating black hole model with Dehnen profiles and evaluates observable differences, especially in weak deflection angles, to identify dark matter profile types.

Findings

Weak deflection angle effectively differentiates dark matter profiles.

Black hole properties show minimal deviation between cored and cuspy profiles.

Black hole mass influences the detectability of dark matter profile effects.

Abstract

There had been recent advancement toward the detection of ultra-faint dwarf galaxies, which may serve as a useful laboratory for dark matter exploration since some of them contains almost 99$\%$ of pure dark matter. The majority of these galaxies contain no black hole that inhabits them. Recently, there had been reports that some dwarf galaxies may have a black hole within. In this study, we construct a black hole solution combined with the Dehnen dark matter halo profile, which is commonly used for dwarf galaxies. We aim to find out whether there would be deviations relative to the standard black hole properties, which might allow determining whether the dark matter profile in an ultra-faint dwarf galaxy is cored or cuspy. To make the model more realistic, we applied the modified Newman-Janis prescription to obtain the rotating metric. We analyzed the black hole properties such as the event horizon, ergoregion, geodesics of time-like and null particles, and the black hole shadow. Using these observables, the results indicate the difficulty of distinguishing whether the dark matter is cored or cuspy. To find an observable that can potentially distinguish these two profiles, we also calculated the weak deflection angle to examine the effect of the Dehnen profile in finite distance and far approximation. Our results indicate that using the weak deflection angle is far better, in many orders of magnitude, in potentially differentiating these profiles. We conclude that although dwarf galaxies are dark matter-dominated places, the effect on the Dehnen profile is still dependent on the mass of the black hole, considering the method used herein.