Physics of Black Hole Spins

Dear Colleagues,

Spin, mass, and (often astrophysically negligible) charge form the trio of parameters that describe black holes in general relativity. While black hole masses can be measured through a variety of dynamical methods, reliably determining spin remains a significant challenge. Yet, understanding spin is deeply connected to many forefront areas of research, including black hole formation, accretion physics, jet launching, and gravitational wave emission.

This Special Issue, “Physics of Black Hole Spins,” brings together cutting-edge approaches from across the multimessenger landscape and distills them into a concise reference for anyone investigating black hole angular momentum, whether through X-ray spectroscopy, gravitational waves, or horizon-scale imaging. It explicitly highlights the current challenges limiting each method and the perspectives most likely to drive future progress. Articles will lay out the shared astrophysical principles underpinning these techniques, clarify how spin imprints on multimessenger signals, and link today’s hurdles to mission-level science goals for facilities such as Athena, the Event Horizon Telescope, the LIGO–Virgo–KAGRA network, and future missions like NewAthena, LISA, and BHEX.

This volume gathers primers, best-practice guides, and comparative assessments that bridge high-resolution X-ray spectroscopy, horizon-scale imaging, and waveform-based spin extraction techniques. Contributors will spotlight the strengths and limitations of current modeling pipelines, share benchmark datasets, and provide transparent treatments of selection effects across X-ray binaries, supermassive black holes, and merging binaries. The resources are designed both to help specialists engage productively across disciplines and to chart a unified, forward-looking path toward percent-level spin precision. We are especially interested in submissions that situate current techniques within the broader context of mission-driven science goals for existing and future observatories. By collating primers, benchmarks, and interdisciplinary perspectives, this Special Issue aims to serve both as a resource for specialists and as a roadmap for the field’s evolution. We look forward to your contributions to this timely and impactful collection.

Dr. George Wong
Dr. Alejandro Cárdenas-Avendaño
Dr. Delilah Gates
Dr. Javier Garcia
Guest Editors

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• black hole spin
• X-ray spectroscopy
• gravitational waves
• horizon-scale imaging
• multimessenger astrophysics
• waveform modeling
• black hole binaries
• spin evolution