Black Hole Spacetime Reconstruction from Galactic Rotation Curves: Thermodynamic Properties and Implications
Year: 2026
Type: preprint
Abstract: We study how the dark-matter environment of a galaxy, reconstructed directly from its observed rotation curve, affects the black hole at its centre. Using the rotation curve of the spiral galaxy NGC\,5907, we construct a general-relativistic model of its halo. The halo has a positive, outward-decreasing density, satisfies the null energy condition, and reproduces the galaxy's dynamical mass of about $3.3\times10^{11}M_\odot$ within 30\,kpc. We then embed a central black hole in this halo and derive its horizon, Hawking temperature, entropy, heat capacity, photon sphere and shadow. Because the halo's gravitational field is weak, all these quantities differ from those of an isolated Schwarzschild black hole by less than one part in $10^{5}$. The heat capacity remains negative, so the black hole stays thermodynamically unstable. For a black hole of $10^{8}M_\odot$, the shadow would span about 0.6\,microarcseconds. Archival WISE infrared photometry confirms, as expected, that the black hole leaves no imprint on the galaxy's light on kiloparsec scales.
Source: arXiv (Cornell University)
Authors: Sanyal, Aritra, Rahaman, Farook
Institution: Jadavpur University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G2958106327, G314647397
OpenAlex ID: W7213506222