Signatures of a de Sitter-core black hole in ringing, transmission and optical appearance

TL;DR

This paper studies a black hole with a de Sitter core, analyzing its horizon structure, scalar perturbations, Hawking radiation, and optical appearance, revealing how the core affects observable properties.

Contribution

It introduces a detailed analysis of a de Sitter-core black hole, including horizon structure, quasinormal modes, greybody factors, and optical signatures, highlighting deviations from Schwarzschild black holes.

Findings

Two horizons exist below a critical core scale-to-mass ratio.

Increasing the core size lowers the scalar potential peak and shifts quasinormal modes.

Larger cores reduce Hawking temperature and mildly diminish the shadow brightness.

Abstract

We investigate a static, asymptotically flat black hole whose central region approaches a de Sitter vacuum. The geometry is controlled by the ADM mass $M_0$ and a core scale $R$, and is generated by an exponentially decaying anisotropic source. After clarifying the stress tensor and the horizon structure, we study scalar-field perturbations, greybody transmission, Hawking emission and the optical image produced by an optically thin infalling flow. The horizon analysis shows that two horizons exist below the critical value $R/M_0\simeq0.7768$, where they merge into an extremal configuration. Increasing the core scale lowers the peak of the scalar effective potential and shifts the quasinormal spectrum away from the Schwarzschild value, with the largest fractional deviations occurring for low multipoles and higher overtones within the WKB domain of validity. The greybody bound indicates stronger filtering as the core becomes more extended, while the QNM--greybody correspondence gives a complementary estimate of the transmission probability in the eikonal regime. The Hawking temperature decreases as the extremal configuration is approached, suppressing the emission rate and shifting its maximum to lower frequencies. Finally, ray-traced intensity profiles show that the apparent shadow and brightness distribution are mildly reduced by a larger de Sitter core.