Influence of observer’s inclination and spacetime structure on photon ring observables
Bibliographic record
Abstract
Recent millimeter-wavelength observations of the near-horizon regions of $\mathrm{M}{87}^{*}$ and Sgr ${\mathrm{A}}^{*}$ by the Event Horizon Telescope have significantly advanced our understanding of gravity and astrophysics under extreme conditions. A key goal for future observations, with improved angular resolution and sensitivity, is the detection of the photon ring in these black holes. For Kerr black holes, photon rings exhibit universal scaling relations in terms of purely geometric observables: the demagnification exponent, time delay, and rotation parameter. Our study employs a nonperturbative, parametrized spinning spacetime to investigate how these observables vary with deviations from the no-hair theorem and the observer's inclination. Particular emphasis is placed on polar observers, which is highly relevant for $\mathrm{M}{87}^{*}$. Our findings reveal that these observables encode vital information about the strong-field spacetime structure, including the morphology of the ergosphere. By analyzing specific non-Kerr spacetimes, we demonstrate that potential measurements of these observables, including the shadow size, can directly constrain the spin and Kerr-deviation functions. For polar observers, time delay measurements offer an independent estimate of the shadow size, providing a complementary probe of the black hole's geometry. These results highlight the potential of using photon rings for precision tests of general relativity and for constraining strong-field deviations from Kerr spacetime.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".