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arXiv · 2512.00917

Probing the Scalar Hair of Rotating Horndeski Black Holes through Thick Disk Images

Qian Wan·Yehui Hou·Minyong Guo
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Abstract

Horizon-scale images of black holes provide a potential probe of fundamental physics, including tests of gravity and black hole hair. To assess the impact of scalar hair on accretion-flow imaging self-consistently, we construct an analytical model of a geometrically thick, magnetized disk around a rotating hairy black hole in Horndeski theory and analyze its 230 GHz image morphology. We find that scalar hair modestly alters the inflow and magnetic-field structure but strengthens gravitational redshift, markedly reducing the total flux and lensed ring brightness through relativistic transfer and spectral-shift effects. Moreover, we highlight a previously unexplored channel: the maximum interferometric diameter of the first photon ring responds strongly to the hair parameter but shows little dependence on accretion-flow details, making it a promising observable for constraining black-hole hair with future space-based interferometry.

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Qian Wan, Yehui Hou, Minyong Guo. 2025-11-30. Probing the Scalar Hair of Rotating Horndeski Black Holes through Thick Disk Images. https://arxiv.org/abs/2512.00917

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