Supermassive black hole in NGC 4649 (M60) with a dark matter halo: Impact on shadow measurements and thermodynamic properties

TL;DR

This study models black holes within dark matter halos in NGC 4649, revealing how dark matter influences black hole properties, shadows, and thermodynamics, with implications for observational measurements.

Contribution

It introduces two extended spacetime solutions for black holes with dark matter halos, analyzing their impact on shadow size and thermodynamic properties, advancing understanding of dark matter effects on black holes.

Findings

Dark matter halo modifies event horizon and spacetime curvature.

Black hole shadow radius slightly increases due to halo influence.

Thermodynamic properties are affected by dark matter parameters.

Abstract

We investigate black hole (BH) solutions embedded in a dark matter (DM) halo, modeled as extensions of the Schwarzschild metric. The DM density profile is constrained by Hubble Space Telescope data, stellar dynamics, and globular cluster (GC) measurements of the elliptical galaxy NGC 4649 (M60). Using this profile, we construct two distinct spacetime solutions characterized by the black hole mass ($M$), critical velocity ($V_c$), and core radius ($a$), all reducing to the Schwarzschild case in the limit $V_c=0$ and $a=0$. Our results show that the DM halo modifies essential BH features, such as the event horizon radius and spacetime curvature, as reflected in the Kretschmann scalar. We also derive an approximate analytical expression for the BH shadow radius, which increases slightly due to the halo's influence. Comparisons with two observational datasets further validate the analysis. Thermodynamic properties are examined across the two models. In the first, a generalized Smarr formula is obtained via two additional variables, $\gamma$ and $a$. The second incorporates halo effects through $V_c=0$ and $a=0$. These results underscore the role of DM in shaping both geometric and thermodynamic aspects of BHs.