Optical Observables of a Hayward Regular Black Hole Surrounded by a Hernquist Dark Matter Halo: Vacuum and Einstein Cluster Models
Alvin Dior Al Ghifari (a*), M. Fahmi Fauzi (a), Handhika S. Ramadhan (a), Anto Sulaksono (a)

a) Departemen Fisika, FMIPA, Universitas Indonesia, Depok 16424, Indonesia
*alvindior[at]gmail.com

Abstract

This study investigates the optical observables of a Hayward regular black hole surrounded by a dark matter halo with the Hernquist density profile. The Hayward metric incorporates a regularization parameter that replaces the central singularity with a de Sitter core, ensuring a singularity-free interior. To model the dark matter halo, we compare two physically distinct frameworks: the vacuum dark matter model, which assumes negative radial pressure and a vanishing shift function, and the Einstein Cluster model, which assumes zero radial pressure and introduces a non-trivial shift function. For both frameworks, the spacetime geometry is derived analytically from the Einstein field equations, with the Hernquist profile modified by a near-horizon cutoff. The photon sphere radius and shadow radius are then computed across a range of regularization parameter and dark matter halo mass values. The Einstein Cluster model exhibits greater shadow radius sensitivity to halo mass compared to the vacuum model. Finally, numerical ray-tracing simulations produce black hole images that reveal qualitatively distinguishable visual features between the two dark matter descriptions.

Keywords: Hayward regular black hole, dark matter halo, Hernquist density profile, Einstein Cluster model, photon sphere, shadow radius, ray-tracing

Topic: Theory, Nuclear, and Particle Physics