Can absorption enhance differences between black-hole images?
Abstract
We investigate whether absorption can enhance morphological differences between images of different spacetimes, particularly when their critical impact parameters are similar. Using a phenomenological thick-accretion-flow model with an effective absorption coefficient χ0, we compare Schwarzschild black-hole images with those of Bardeen, Hayward, and Ayón-Beato--García black holes. In the face-on Schwarzschild--Bardeen comparison with g/M=0.5, the dominant brightness shifts from a narrow lensed feature to a broader outer feature at χ0M≃0.585 and 0.717, respectively. Near the first transition, the integrated difference between independently normalized images increases by $23.5$% on a common physical grid and by $46.6$% after rescaling by the respective critical impact parameters. Enhancement occurs across all three regular-black-hole families and over a broad range of the sampled flow parameters and viewing inclinations, although its magnitude and occurrence depend on the prescribed flow. Asynchronous brightness-peak transitions alone are insufficient to guarantee enhancement. These results suggest that the opacity dependence of image morphology may provide information complementary to the critical-curve scale, potentially helping distinguish spacetimes with similar characteristic shadow sizes. Assessing this possibility observationally requires physically consistent, frequency-dependent radiative transfer.
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BibTeX
@misc{li2026absorption,
title = {{Can absorption enhance differences between black-hole images?}},
author = {Tong Li and Jian-Yun Wan and Zi-Liang Wang},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07544},
eprint = {2611.07544},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07544},
}
RIS
TY - UNPB
TI - Can absorption enhance differences between black-hole images?
AU - Tong Li
AU - Jian-Yun Wan
AU - Zi-Liang Wang
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.07544
UR - https://arxiv.org/abs/2611.07544
AB - We investigate whether absorption can enhance morphological differences between images of different spacetimes, particularly when their critical impact parameters are similar. Using a phenomenological thick-accretion-flow model with an effective absorption coefficient χ_0, we compare Schwarzschild black-hole images with those of Bardeen, Hayward, and Ayón-Beato--García black holes. In the face-on Schwarzschild--Bardeen comparison with g/M=0.5, the dominant brightness shifts from a narrow lensed feature to a broader outer feature at χ_0M≃0.585 and 0.717, respectively. Near the first transition, the integrated difference between independently normalized images increases by $23.5$% on a common physical grid and by $46.6$% after rescaling by the respective critical impact parameters. Enhancement occurs across all three regular-black-hole families and over a broad range of the sampled flow parameters and viewing inclinations, although its magnitude and occurrence depend on the prescribed flow. Asynchronous brightness-peak transitions alone are insufficient to guarantee enhancement. These results suggest that the opacity dependence of image morphology may provide information complementary to the critical-curve scale, potentially helping distinguish spacetimes with similar characteristic shadow sizes. Assessing this possibility observationally requires physically consistent, frequency-dependent radiative transfer.
ER -