English

Signature of iron line profile from a Kerr-like wormhole

High Energy Astrophysical Phenomena 2026-04-28 v2 General Relativity and Quantum Cosmology

Abstract

Broad, skewed iron Kα\alpha emission lines in the X-ray spectra of accreting black holes encode key information about the spacetime geometry of the innermost disk. While the Kerr metric is standard for spin measurements, horizonless alternatives like traversable "Kerr-like" wormholes can mimic many black hole signatures, challenging current data interpretations. We develop a relativistic reflection framework incorporating Kerr-like wormhole geometries to predict iron line distortions and assess the feasibility of distinguishing event horizons from wormhole throats.Using a custom ray-tracing subroutine, we implement two \textsc{XSPEC} modules: \texttt{kwline} for δ\delta-function profiles and \texttt{kwconv} for full reflection spectra, parameterized by spin, throat radius, and shape-function coefficients. We compute a dense grid of line profiles and generate synthetic \textit{NuSTAR} spectra with realistic response matrices. By fitting these simulations with canonical Kerr models, we quantify deviations attributable to wormhole geometries.We find that Kerr-like wormholes produce narrower Fe Kα\alpha lines with suppressed red wings as the throat parameter λ\lambda increases. In 50 ks \textit{NuSTAR} simulations (λ=0.9,a=0.998\lambda=0.9, a_*=0.998), simple convolutional models (\texttt{kerrconv}) can mimic the wormhole spectrum. However, self-consistent models like \texttt{relxillCp} result in statistical failure, yielding structured residuals and unphysical parameter pegging (e.g., emissivity qin10q_{\rm in} \to 10). We conclude that large-throat wormholes are detectable in high-quality X-ray spectra if analyzed with fully consistent reflection models rather than post-processing approximations.

Keywords

Cite

@article{arxiv.2604.22268,
  title  = {Signature of iron line profile from a Kerr-like wormhole},
  author = {Cheng Liu and Hoongwah Siew and Hong-Xuan Jiang and Yosuke Mizuno and Tao Zhu},
  journal= {arXiv preprint arXiv:2604.22268},
  year   = {2026}
}

Comments

Accepted for publication in A&A. 17 pages, 20 figures