Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

TL;DR

This paper explores how supermassive black holes surrounded by dark matter modeled as an anisotropic fluid can explain observed QPOs in active galactic nuclei through epicyclic oscillations, extending the geodesic model beyond vacuum black holes.

Contribution

It introduces a new exact solution for dark matter around black holes and applies epicyclic resonance models to explain QPOs in galactic nuclei.

Findings

The model can fit observed QPOs in most active galactic nuclei.

Epicyclic frequencies depend on dark matter halo parameters.

Standard vacuum black hole models are insufficient for some QPO observations.

Abstract

Recently introduced exact solution of the Einstein gravity coupled minimally to an anisotropic fluid representing dark matter can well represent supermassive black holes in galactic nuclei with realistic distribution of dark matter around the black hole, given by the Hernquist-like density distribution. For these fluid-hairy black hole spacetimes, properties of the gravitational radiation, quasinormal ringing, and optical phenomena were studied, giving interesting results. Here, using the range of physical parameters of these spacetimes allowing for their relevance in astrophysics, we study the epicyclic oscillatory motion of test particles in these spacetimes. The frequencies of the orbital and epicyclic motion are applied in the epicyclic resonance variant of the geodesic model of quasiperiodic oscillations (QPOs) observed in active galactic nuclei to demonstrate the possibility to solve the cases where the standard vacuum black hole spacetimes are not allowing for explanation of the observed data. We demonstrate that the geodesic model can explain the QPOs observed in most of the active galactic nuclei for the fluid-hairy black holes with reasonable halo parameters.