Dark matter halos and transonic accretion flow

TL;DR

This work investigates how surrounding dark matter halos, including central density spikes, modify the spacetime and influence hot, radiatively inefficient accretion onto galactic supermassive black holes. It models the environment with an anisotropic DM stress-energy tensor using the Einstein-cluster framework and solves for $f(r)$ and $m(r)$ across DM profiles, enforcing a scale hierarchy $M_{BH} ≤ M_{halo} ≤ a_0$. For steady, axisymmetric transonic flows with a variable adiabatic index $Γ$, it identifies a critical point at $r_c$ and shows the DM halo shifts $r_c$ inward and elevates the disk temperature, boosting luminosity. Predicted spectral energy distributions and bolometric luminosities exhibit substantial enhancement relative to a pure Schwarzschild case, scaling with halo mass $M_{halo}$ and compactness $M_{halo}/a_0$, offering an observational avenue to probe dense DM near galactic centers and its role in SMBH–galaxy coevolution.

Abstract

The interplay between supermassive black holes (SMBHs) and their surrounding environment is fundamental to understanding galactic evolution. This work investigates the influence of a cold dark matter (DM) halo on the dynamics of relativistic, low angular momentum, inviscid, and advective hot accretion flow onto a galactic SMBH. Modeling the spacetime geometry as a black hole embedded within various DM distributions, including those with a central density spike, we demonstrate that the presence of a DM halo, particularly one that is massive and compact, enhances the luminosity of the accretion disk. The dominant contribution to this luminosity originates from the inner regions of the flow, suggesting that luminosity measurements could serve as a valuable observational probe for the dense DM environments expected near galactic centers.

Figures (2)

• Figure 1: A plot showing the different DM density profiles (Hernquist, NFW, Einasto, Spike) as a function of radial distance. The spike model shows a significant density enhancement close to the black hole. See Chowdhury:2025tpt for details.
• Figure 2: Top: plot of the spectral energy distribution for different DM distributions for different values scale radius: $M_{\rm halo}=100 M_{\rm BH}, a_0=10^6 M_{\rm BH}$ (left), $M_{\rm halo}=100 M_{\rm BH} \hbox{and} a_0=10^4 M_{\rm BH}$ (right). Halo compactness $(M_{\rm halo}/a_0)$ changes from $10^{-4}$ (left) to $10^{-2}$ (right) for a fixed halo mass. The solid black curve in each plot shows the SED for a Schwarzschild BH of the same mass. The insets show the location of the peak of the SEDs in each case. The flow parameters are $\lambda=3.674$ and $\mathcal{E}=1.001$. Bottom: plot of bolometric luminosity for different dark matter profiles with halo compactness, $M_{\rm halo}/a_0$ for $M_{\rm halo}=100 M_{\rm BH}$ for $\mathcal{E}=1.001$ and $\lambda=3.674$ (left). Plot of the luminosity for different dark matter profiles with $M_{\rm halo}$ for $M_{\rm halo}/ a_0=0.01$ (right) for the same values of energy and specific angular momentum of the flow.