Dynamics of photons and shadows for black holes haired with parity-odd fields

TL;DR

This paper investigates how parity-odd scalar hair affects black hole shadows, revealing measurable differences from Kerr black holes that could be detected by current or future observational efforts.

Contribution

It provides the first systematic analysis of photon dynamics and shadow features for black holes with parity-odd scalar hair using ray-tracing methods.

Findings

Scalar-haired black hole shadows differ measurably from Kerr black holes.

Differences are detectable even with tiny scalar charges.

Some scalar-haired black holes are within Event Horizon Telescope observational uncertainties.

Abstract

Strong self-gravitational fields enable the realization of macroscopic odd-parity quantum objects. Using ray-tracing methods, we systematically analyze the dynamics of photons and the shadow features of rotating black holes with parity-odd scalar hair and contrast them with those of Kerr black holes. Our results demonstrate measurable distinctions between scalar-haired black hole shadows and their Kerr counterparts. Notably, even for tiny scalar charge and negligible scalar hair mass contributions, these differences remain quantitatively resolvable. In particular, one of the hairy black hole reported here lies within the Event Horizon Telescope observational uncertainties, probing the scalar masses of $1.02\times10^{-20}$eV with M87*. These findings may provide related theoretical benchmarks for future observational campaigns targeting scalar-field dark matter candidates through black hole shadow imaging.