{"id":"70900ab2-6b2e-463d-aaf8-4a4feb20949b","arxiv_id":"2607.18751","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"JP black holes with non-closed horizons produce an 'extended inner shadow' distinct from the ordinary inner shadow, and all image scales (inner shadow, photon ring, peak positions) grow monotonically with |ϵ3|.","lead":"Using numerical backward ray-tracing, this paper computes images of thin accretion disks around Johannsen-Psaltis (JP) black holes — Kerr-like metrics with a deviation parameter ϵ3. For non-closed 'dumbbell' horizons it reports a new dark feature, an extended inner shadow, and maps how image, intensity, and Doppler structure depend on ϵ3.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Extended inner shadow may be an artifact of setting the disk inner edge at r_h^Kerr; no sensitivity test is provided.","rationale":"The reader's weakest assumption is the most load-bearing concern. The paper's central claim is that a non-closed JP horizon produces a new, qualitatively distinct extended inner shadow. But in a thin-disk image, dark regions inside the photon ring are determined by the disk's emission cut-off: a photon can only illuminate a pixel if it crossed the disk at some r ≥ r_in. For a genuine event horizon the cut-off is immaterial, since no photons emerge from inside the horizon. Here there is no horizon, so the choice r_in = r_h^Kerr is doing real work. The paper explicitly acknowledges this is an assumption and provides no sensitivity analysis. The truncated analytical framework in Sec. 3.3 is a secondary concern: even if the formation mechanism is derived correctly, the numerical result would still be conditional on the disk-edge prescription. The 'infinite coordinate time' property imported from Ref. [47] is also untested here, but it only matters if one wants to argue that emission from inside r_h^Kerr is invisible; the direct, minimal test is to extend the disk inward and see whether the extended shadow persists. I agree with the reader's CONDITIONAL verdict: the claim is plausible and internally consistent, but it cannot be accepted as a robust new feature without this sensitivity check or the release of the ray-tracing code/data. My verdict is UNCHANGED relative to the reader because the conditionality already captures this concern.","tokens_in":46555,"tokens_out":5236,"duration_ms":50516,"concrete_test":"Recompute the non-closed-horizon images (e.g., a=0.9, ϵ3=2) with the disk inner edge varied across at least three choices: r_in = r_h^Kerr (the paper's choice), r_in = r_ISCO_retro (the physically motivated thin-disk inner edge), and r_in = 0.1M (well inside r_h^Kerr), keeping the emissivity law, observer position, and all other settings fixed. Measure the linear size or area of the extended inner shadow as a function of r_in. If the extended shadow shrinks or disappears for smaller r_in, it is a truncation artifact and the central claim fails. If it remains unchanged for all r_in below r_h^Kerr, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central novelty — an 'extended inner shadow' for non-closed horizons — is a property of the assumed emission region as much as of the spacetime. In Sec. 3.3 the disk inner boundary is fixed at r_in = r_h^Kerr because 'a well-defined event horizon does not exist in the non-closed configuration,' but no physical mechanism (ISCO, photon surface, causality boundary) selects this radius. The spacetime interior to r_h^Kerr is regular up to the naked singularity and could in principle support emitting matter; the only argument for its invisibility is an imported 'infinite coordinate time' result from the authors' prior work, not re-derived here. If any dark pixels that form the extended inner shadow are dark only because the disk was artificially truncated at r_h^Kerr, the headline feature is not a new spacetime shadow but a boundary artifact. The paper neither varies r_in nor reports how the extended-shadow size depends on it. The reader's weakest assumption identifies exactly this point, and the paper's own language ('reasonable to assume') concedes its ad hoc character.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper constructs images of Johannsen-Psaltris black holes surrounded by thin, optically thin accretion disks using numerical backward ray-tracing. For closed-horizon JP black holes it systematically studies how the inner shadow, photon ring, intensity profiles, directional scales, ellipticities, and redshift/blueshift maps depend on the deviation parameter ϵ3 for selected spins and observer inclinations. For non-closed horizon configurations it reports a new 'extended inner shadow' and proposes an approximate analytical formation mechanism in Sec. 3.3.","tokens_in":46686,"tokens_out":4498,"duration_ms":48604,"significance":"The claimed extended inner shadow, if robust, would be a qualitative image feature absent in Kerr and traceable to the JP deviation parameter, giving a new observable avenue for no-hair tests. The closed-horizon analysis has real strengths: the image quantities are computed by geodesic integration rather than fitted, the photon-ring peak is honestly excluded from quantitative claims because of resolution sensitivity, and the model inherits ϵ2=0 from LLR/PPN constraints. The non-closed-horizon claim, however, is not yet established because the imaging result depends on an ad hoc choice of the disk inner edge.","major_comments":[{"comment":"The headline 'extended inner shadow' is computed with the thin disk truncated at the Kerr horizon radius r_h^Kerr. For a non-closed JP horizon the spacetime interior to r_h^Kerr is regular up to the naked singularity, so there is no geometric reason why emitting matter must end there; no ISCO, photon-surface, or causality argument is used to select this radius. A dark region is produced whenever the backward-traced geodesic intersects the equatorial plane at r < r_in simply because no emitter exists there. The feature may therefore be a disk-truncation artifact rather than a new spacetime shadow. The paper should test the sensitivity of the extended-shadow size and intensity to r_in (e.g., r_in = 0.5, 0.8, 1.2 r_h^Kerr) and report how the claimed mechanism in Sec. 3.3 depends on this choice. Without such a test the central claim is not load-bearing.","section":"Sec. 3.3, inner-disk-edge prescription r_in = r_h^Kerr"},{"comment":"The paper uses the statement that photons from the vicinity of the naked singularity require infinite coordinate time to reach infinity as justification for neglecting the singular region in the non-closed case. This result is imported from the authors' previous work and not re-derived; it should be stated precisely or re-derived in the present framework. More importantly, even if the singularity itself is unobservable, this does not exclude emitting matter in the regular region r < r_h^Kerr. The actual assumption behind the extended inner shadow is the absence of emission interior to r_h^Kerr, and that assumption is neither physically derived nor numerically varied.","section":"Sec. 2, paragraph after Fig. 1, and Sec. 3.3"}],"minor_comments":[{"comment":"Typo: 'analytic deviation of photon trajectories' should be 'analytic derivation of photon trajectories.'","section":"Introduction, Sec. 2"},{"comment":"The caption/text color coding is inconsistent: the text describes yellow, green, cyan, and red regions, while the caption mentions black, yellow, green, blue, and red. Please align the labels.","section":"Fig. 3 and text"},{"comment":"The notation I0 is used both for the observed intensity and for the Lorentz-invariant intensity at the observer; please distinguish these, for example with a different symbol or explicit subscript.","section":"Eqs. (3.14)-(3.23)"},{"comment":"The text refers to Fig. 5 when discussing the evolution of average radii and relative deviations; the relevant figure appears to be Fig. 4. Please correct the cross-reference.","section":"Sec. 3.2, discussion of average radii"},{"comment":"Setting f_n = 1 is an arbitrary normalization. The paper states that f_n mainly affects photon-ring brightness, and it excludes photon-ring peaks from quantitative claims, which mitigates the concern; however, this should be stated more explicitly so that the absolute intensity scale is not over-interpreted.","section":"Eq. (3.23) and fudge factor f_n"}],"recommendation":"major_revision","confidential_remarks":"The extended inner shadow is the main novelty and the part most likely to attract interest, but it currently rests on an untested disk inner-edge assumption. I would recommend requesting a robustness study over r_in as a condition for publication. The prose is also extremely repetitive and could be shortened substantially without loss of content."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read the paper. The numerical work is competent, and the closed-horizon part reads as a solid extension of the authors' earlier shadow study to thin-disk images. The systematic dependence of shadow radius, ellipticity, and Doppler maps on ϵ3 is new and internally consistent; I did not spot contradictions. The honesty about excluding the resolution-sensitive photon-ring peak from quantitative claims is welcome. That part earns its keep.\n\nThe headline feature is the extended inner shadow for non-closed horizons. Here the paper is on shakier ground. The feature is defined as the dark region between the disk inner edge and the photon ring, but the inner edge is set to r_h^Kerr simply because there is no horizon in that parameter regime. The text calls this 'reasonable to assume' but gives no physical mechanism. If the disk were allowed to emit from inside r_h^Kerr, the dark region would likely shrink or disappear. The paper does not report a sensitivity test, and the stress-test note is correct: the extended inner shadow may be a boundary artifact rather than a genuine spacetime shadow. That makes the central claim conditional at best.\n\nThere are two additional weaknesses. The analytical framework in Sec. 3.3 is presented but truncated; as provided, I cannot verify it. And there is no code, data, or error bars for the quantitative claims, so independent checks are not straightforward. The reliance on the authors' own prior result for the naked singularity behavior is acceptable if that result is solid, but it is not re-derived here.\n\nWho is this for? People working on black hole imaging in parametrized deviations from Kerr. The closed-horizon catalog, the intensity peak trends, and the Doppler maps are of practical use. The extended inner shadow, if it survives a sensitivity analysis, would be a nice qualitative observable. As it stands, I would not cite the headline feature in my own work until the inner-edge choice is justified or varied. I would, however, send this to a serious referee: the core machinery appears sound, the question is well-posed, and a referee could reasonably request the missing tests. The paper is not sloppy; it is just incomplete at the key point.","headline":"Solid numerical imaging catalog, but the headline extended inner shadow may be an artifact of an untested disk inner-edge choice.","tokens_in":47314,"tokens_out":1967,"would_cite":false,"duration_ms":19484,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":["83C57","83C10"],"pacs":[],"model":"deepseek-v4-flash","headline":"The JP black hole with a non-closed horizon shows an extended inner shadow absent in Kerr images.","keywords":["Johannsen-Psaltis metric","black hole image","inner shadow","thin accretion disk","backward ray-tracing","deviation parameter","Kerr hypothesis","no-hair theorem"],"falsifier":"For a non-closed JP horizon, move the disk inner edge inward from r_h^Kerr (e.g., to half or to the singularity region) and re-run the ray-tracing; if the extended inner shadow disappears, it is an artifact of the disk inner-edge prescription.","tokens_in":1398,"feed_emoji":"🕳️","tokens_out":2788,"duration_ms":66948,"temperature":0.7,"pith_summary":"The paper uses numerical backward ray-tracing to image Johannsen-Psaltis (JP) black holes with thin accretion disks. It shows that when the JP deviation parameter ε3 makes the event horizon non-closed, the image contains an extended inner shadow beyond the ordinary inner shadow, a feature with no Kerr analogue. For closed horizons, increasing |ε3| enlarges the inner shadow faster than the photon ring, narrowing the direct-image band, and the growth is anisotropic, strongest along the direction probing the equatorial plane. These features are presented as observable signatures to test the Kerr paradigm and the no-hair theorem.","feed_headline":"Deformed black holes gain an extra inner shadow layer","feed_subtitle":"A single deviation parameter reshapes the photon image, offering a test of whether astrophysical black holes are Kerr.","key_machinery":"The single deviation parameter ε3 enters the JP metric through h(r,θ)=ε3 M^3 r/Σ^2. Its angular dependence (largest at the equator, smallest at the poles) plus frame-dragging drives the anisotropic image deformation. Because JP spacetime is Petrov type I, photon motion is non-separable, so images are computed by numerical backward ray-tracing with a ZAMO frame and simplified radiative transfer.","core_discovery":"The paper finds a new image feature: an extended inner shadow, distinct from the original inner shadow, in images of JP black holes whose event horizon is non-closed (dumbbell-shaped with an exposed singularity). Using backward ray-tracing and an approximate analytical framework, it shows the feature arises from the ε3 deviation. For closed horizons, the inner-shadow growth outpaces the photon-ring growth, and the evolution is dominated by the equatorial-plane direction where h(r,θ) is largest.","pith_inferences":["The extended inner shadow's existence depends on the disk inner edge being at the Kerr horizon radius; other choices might alter or erase it.","The directional anisotropy predicts that shadow ellipticity relative to the spin axis encodes ε3, offering a testable extension.","Further work could turn the approximate analytical framework into a closed-form relation between shadow size and ε3 for fast parameter estimation."],"forward_implications":["Non-closed horizons produce an extended inner shadow, a direct image marker absent in Kerr.","Closed horizons: increasing |ε3| expands both inner shadow and photon ring, with the inner shadow catching up.","The growth anisotropy is tied to the equatorial plane, giving a geometric signature of ε3.","Maximum-blueshift position responds to ε3 in prograde but not retrograde flows.","These relations can be used to constrain deviations from Kerr with VLBI images."],"fun_headline_variants":["Non-closed horizons cast a second inner shadow","Deviated Kerr black holes show extra shadow feature","New shadow marks departure from Kerr geometry","JP black holes: an extended inner shadow revealed","Exposed singularity triggers a deeper shadow"],"cache_read_input_tokens":48512,"weakest_assumption_plain":"The extended inner shadow rests on assuming the thin disk stops at the Kerr horizon radius r_h^Kerr for non-closed horizons; there is no sensitivity test of that choice.","fun_headline_variants_meta":{"raw":{"variants":["Non-closed horizons cast a second inner shadow","Deviated Kerr black holes show extra shadow feature","New shadow marks departure from Kerr geometry","JP black holes: an extended inner shadow revealed","Exposed singularity triggers a deeper shadow"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000203,"raw_usage":{"total_tokens":1198,"prompt_tokens":692,"completion_tokens":506,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":436,"completion_tokens_details":{"reasoning_tokens":452}},"tokens_in":436,"tokens_out":506,"duration_ms":5527,"temperature":1.0,"reasoning_tokens":452,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T14:28:17.590340+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"For a non-closed JP horizon, move the disk inner edge inward from r_h^Kerr (e.g., to half or to the singularity region) and re-run the ray-tracing; if the extended inner shadow disappears, it is an artifact of the disk inner-edge prescription.","supporting_citations":[],"review_version":1}