{"total":15,"items":[{"citing_arxiv_id":"2605.19731","ref_index":60,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Neutron stars more compact than black holes in quasi-topological gravity: Equilibrium configurations and radial stability","primary_cat":"gr-qc","submitted_at":"2026-05-19T12:05:32+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"In quasi-topological gravity, neutron stars can surpass black-hole compactness with universal high-density behavior and theory corrections that stabilize radially unstable configurations from general relativity.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2605.13901","ref_index":19,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"On the impossibility of observational confirmation of black holes","primary_cat":"gr-qc","submitted_at":"2026-05-12T18:41:08+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":3.0,"formal_verification":"none","one_line_summary":"No observational data can confirm the existence of black holes because general relativity imposes fundamental limits on what can be established about them.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2604.15260","ref_index":29,"ref_count":1,"confidence":0.9,"is_internal_anchor":false,"paper_title":"Taming the Aretakis instability: extremal black holes with multi-degenerate horizons","primary_cat":"gr-qc","submitted_at":"2026-04-16T17:36:55+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":6.0,"formal_verification":"none","one_line_summary":"Black holes with infinitely degenerate horizons are proposed to be stable against Aretakis instability, potentially serving as end states.","context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"Berti and C. A. R. Herdeiro,Light-Ring Stability for Ultracompact Objects,Phys. Rev. Lett.119(2017) 251102 [1708.04211]. [27] F. Di Filippo,Nature of inner light rings,Phys. Rev. D110(2024) 084026 [2404.07357]. [28] J. Keir,Slowly decaying waves on spherically symmetric spacetimes and ultracompact neutron stars,Class. Quant. Grav.33(2016) 135009 [1404.7036]. [29] V. Cardoso, L. C. B. Crispino, C. F. B. Macedo, H. Okawa and P. Pani,Light rings as observational evidence for event horizons: long-lived modes, ergoregions and nonlinear instabilities of ultracompact objects,Phys. Rev. D90(2014) 044069 [1406.5510]. [30] S. Aretakis,Stability and Instability of Extreme Reissner-Nordström Black Hole Spacetimes for Linear Scalar Perturbations I,Commun."},{"citing_arxiv_id":"2604.15240","ref_index":55,"ref_count":1,"confidence":0.9,"is_internal_anchor":false,"paper_title":"Boson star-black hole binaries: initial data and head-on collisions","primary_cat":"gr-qc","submitted_at":"2026-04-16T17:15:14+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":6.0,"formal_verification":"none","one_line_summary":"A one-body conformal-factor correction stabilizes boson star-black hole initial data, enabling gravitational-wave analysis that shows higher multipoles can discriminate mixed mergers from pure black-hole binaries.","context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"Staelens, \"Search for growing angular modes in ultracompact boson star evolutions,\" J. Phys. Conf. Ser.3177, 012046 (2026), arXiv:2508.19460 [gr-qc]. [54] Tamara Evstafyeva, Nils Siemonsen, and William E. East, \"Assessing the stability of ultracompact spinning boson stars with nonlinear evolutions,\" Phys. Rev. D 113, 044024 (2026), arXiv:2508.11527 [gr-qc]. [55] Xiangyu Wang, Zhenyu Zhang, Hai-Qing Zhang, Miny- ong Guo, and Bin Chen, \"Testing solitonic boson star interpretations of Sagittarius A* with near-infrared flare astrometry,\" (2026), arXiv:2604.21883 [astro-ph.HE]. [56] Argelia Bernal and F. Siddhartha Guzman, \"Scalar Field Dark Matter: Head-on interaction between two structures,\" Phys. Rev. D74, 103002 (2006),"},{"citing_arxiv_id":"2604.14011","ref_index":50,"ref_count":2,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Properties of black holes in non-linear electrodynamics","primary_cat":"hep-th","submitted_at":"2026-04-15T15:56:46+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"Analytic charged black holes in nonlinear electrodynamics with non-monotonic lapse functions support stable light rings and additional longer-lived quasinormal modes compared to Einstein gravity.","context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"and optical appearance of a magnetically charged regular black hole illuminated by various accretion disks,JCAP08(2024) 041 [2406.07300]. [48] J.G. Russo and P.K. Townsend,Causality and energy conditions in nonlinear electrodynamics,JHEP06(2024) 191 [2404.09994]. [49] J.P. Boyd,Chebyshev and Fourier Spectral Methods, Dover Publications, Mineola, New York, 2nd ed. (2001). [50] V. Cardoso, L.C.B. Crispino, C.F.B. Macedo, H. Okawa and P. Pani,Light rings as observational evidence for event horizons: long-lived modes, ergoregions and nonlinear instabilities of ultracompact objects,Phys. Rev. D90(2014) 044069 [1406.5510]. [51] P.V.P. Cunha, E. Berti and C.A.R. Herdeiro,Light-Ring Stability for Ultracompact Objects,Phys. Rev."},{"citing_arxiv_id":"2604.13208","ref_index":92,"ref_count":1,"confidence":0.9,"is_internal_anchor":false,"paper_title":"Axial Oscillations of Viscous Neutron Stars","primary_cat":"gr-qc","submitted_at":"2026-04-14T18:30:45+00:00","verdict":null,"verdict_confidence":null,"novelty_score":null,"formal_verification":null,"one_line_summary":null,"context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"Cunha, Emanuele Berti, and Carlos A. R. Herdeiro, \"Light-Ring Stability for Ultracom- pact Objects,\" Phys. Rev. Lett.119, 251102 (2017), arXiv:1708.04211 [gr-qc]. [91] Pedro V. P. Cunha, Carlos Herdeiro, Eugen Radu, and Nicolas Sanchis-Gual, \"Exotic Compact Objects and the Fate of the Light-Ring Instability,\" Phys. Rev. Lett. 130, 061401 (2023), arXiv:2207.13713 [gr-qc]. [92] Nils Siemonsen, \"Nonlinear Treatment of a Black Hole Mimicker Ringdown,\" Phys. Rev. Lett.133, 031401 (2024), arXiv:2404.14536 [gr-qc]. [93] Gareth Arturo Marks, Seppe J. Staelens, Tamara Evstafyeva, and Ulrich Sperhake, \"Long-term stable nonlinear evolutions of ultracompact black-hole mim- ickers,\" (2025), arXiv:2504.17775 [gr-qc]. [94] Tamara Evstafyeva, Nils Siemonsen, and William E."},{"citing_arxiv_id":"2604.06312","ref_index":24,"ref_count":1,"confidence":0.9,"is_internal_anchor":false,"paper_title":"Black Hole-Boson Star Binaries: Gravitational Wave Signals and Tidal Disruption","primary_cat":"gr-qc","submitted_at":"2026-04-07T18:00:03+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"Numerical simulations of black hole-boson star binaries show that scalar self-interactions can suppress tidal disruption while radiative efficiency depends on the chosen potential.","context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"of BH phenomenology, including shadows [16, 17], po- larimetry imprints [18] and ringdown spectra [19, 20], all of which are closely related to the light-ring structure of the object [21-23]. While UCOs may suffer from a ∗ gam54@cam.ac.uk † ss3033@cam.ac.uk ‡ U.Sperhake@damtp.cam.ac.uk dynamical instability that, if efficient, would limit their viability as astrophysical BH mimickers [24], recent non- linear dynamical evolutions of UCOs have found evidence that the instability may not be generally effective [25-27], adding further credence to their viability as physical ob- jects. Exploring the prospects for an ECO population existing in the Universe requires a detailed understand- ing of how GW signals from mergers involving ECOs (and"},{"citing_arxiv_id":"2601.10806","ref_index":52,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Shadow signatures and energy accumulation in Lorentzian-Euclidean black holes","primary_cat":"gr-qc","submitted_at":"2026-01-15T19:15:58+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"Lorentzian-Euclidean black holes produce excess inner-shadow intensity and accumulate energy at the horizon with backreaction unlike stable light rings.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2512.21535","ref_index":23,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Bulk-cone singularities and echoes from AdS exotic compact objects","primary_cat":"hep-th","submitted_at":"2025-12-25T07:05:58+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":7.0,"formal_verification":"none","one_line_summary":"AdS exotic compact objects imprint bulk-cone singularities from null geodesics and echoes from trapped waves on CFT Green functions, signaling no horizon.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2512.01349","ref_index":12,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"AdS gravastar and its signatures from dual conformal field theory","primary_cat":"hep-th","submitted_at":"2025-12-01T07:02:52+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"AdS gravastar glued from AdS-Schwarzschild and de Sitter yields horizon-less signatures including specific bulk-cone singularities and echoes in dual CFT retarded Green functions.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2511.08692","ref_index":117,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Excitation factors for horizonless compact objects: long-lived modes, echoes, and greybody factors","primary_cat":"gr-qc","submitted_at":"2025-11-11T19:00:08+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":6.0,"formal_verification":"none","one_line_summary":"Excitation factors of long-lived quasinormal modes in horizonless compact objects scale with their small imaginary frequency, suppressing early contributions and producing a hierarchy where prompt ringdown uses ordinary modes and late echoes use cavity modes.","context_count":1,"top_context_role":"background","top_context_polarity":"unclear","context_text":"Destounis, M. Malato Corrˆ ea, C. F. B. Macedo, and R. Panosso Macedo, (2025), arXiv:2509.16310 [gr-qc]. [115] R. F. Rosato, S. Biswas, S. Chakraborty, and P. Pani, Phys. Rev. D111, 084051 (2025), arXiv:2501.16433 [gr- qc]. [116] V. Cardoso, L. C. B. Crispino, C. F. B. Macedo, H. Okawa, and P. Pani, Phys. Rev. D90, 044069 (2014), arXiv:1406.5510 [gr-qc]. [117] P. Bueno, P. A. Cano, F. Goelen, T. Hertog, and B. Ver- cnocke, Physical Review D97(2018), 10.1103/phys- revd.97.024040. [118] S. Chakraborty, E. Maggio, A. Mazumdar, and P. Pani, Phys. Rev. D106, 024041 (2022), arXiv:2202.09111 [gr- qc]. [119] A. A. Starobinskil and S. M. Churilov, Sov. Phys. JETP 65, 1 (1974). [120] E. Maggio, V. Cardoso, S. R. Dolan, and P."},{"citing_arxiv_id":"2510.07467","ref_index":5,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Weakly turbulent saturation of the nonlinear scalar ergoregion instability","primary_cat":"gr-qc","submitted_at":"2025-10-08T19:15:23+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":7.0,"formal_verification":"none","one_line_summary":"Time-domain evolutions demonstrate that the nonlinear scalar ergoregion instability saturates via a weakly turbulent direct cascade transferring energy to small scales and populating higher-order azimuthal modes on the stable light ring.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2508.19460","ref_index":18,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Search for growing angular modes in ultracompact boson star evolutions","primary_cat":"gr-qc","submitted_at":"2025-08-26T22:27:31+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":4.0,"formal_verification":"none","one_line_summary":"The paper decomposes simulation data of ultracompact boson stars into spherical harmonics as a first step toward characterizing non-spherical modes.","context_count":0,"top_context_role":null,"top_context_polarity":null,"context_text":null},{"citing_arxiv_id":"2501.16433","ref_index":108,"ref_count":1,"confidence":0.98,"is_internal_anchor":true,"paper_title":"Greybody factors, reflectionless scattering modes, and echoes of ultracompact horizonless objects","primary_cat":"gr-qc","submitted_at":"2025-01-27T19:00:06+00:00","verdict":"UNVERDICTED","verdict_confidence":"LOW","novelty_score":5.0,"formal_verification":"none","one_line_summary":"High-frequency quasi-reflectionless scattering modes in the greybody factors of ultracompact horizonless objects are responsible for echoes in the time-domain response.","context_count":1,"top_context_role":"method","top_context_polarity":"use_method","context_text":"ECO radius r0 such that, near the effective ra- dius [31, 104, 107] Ψ → e−iω(r∗−r0 ∗) + RECOeiω(r∗−r0 ∗) , r ∗ → r0 ∗ (6) where r0 ∗ = r∗(r0). While our formalism is valid for any RECO(ω), for concreteness in the following we will consider models with constant RECO (where the case of a nondissipative object corresponds to |RECO| = 1), as well as models featuring Boltz- mann reflectivity [108]. The scattering schemes for Schwarzschild-like wormholes and ECOs are depicted in Fig. 1. The surface reflection amplitudes analyzed in this work are presented in Table I. Note that sufficiently com- pact wormhole spacetimes are included in the reflectivity model by imposing Eq. (6) at the throat and using the surface reflection amplitude given in Table I [107]."},{"citing_arxiv_id":"1904.05363","ref_index":85,"ref_count":1,"confidence":0.9,"is_internal_anchor":false,"paper_title":"Testing the nature of dark compact objects: a status report","primary_cat":"gr-qc","submitted_at":"2019-04-10T18:00:05+00:00","verdict":"ACCEPT","verdict_confidence":"MODERATE","novelty_score":2.0,"formal_verification":"none","one_line_summary":"Current and future observations can test whether dark compact objects are Kerr black holes or exotic alternatives, with null results strengthening the black hole paradigm.","context_count":1,"top_context_role":"background","top_context_polarity":"background","context_text":"3 ECO taxonomy: from DM to quantum gravity A nonexhaustive summary of possible self-gravitating compact objects is shown in Table 1. Different objects arise in different contexts. We refer the reader to specific works (e.g., Ref. [108]) for a more comprehensive review of the models. Model Formation Stability EM signatures GWs Fluid stars ✓ ✓ ✓ ✓ [90] [85,88,109-113] [85,109,112,114] Anisotropic stars \u0017 ✓ ✓ ✓ [115-117] [118-120] [115,119,120] Boson stars & ✓ ✓ ✓ ✓ oscillatons [53,54,121-123] [86,124-128] [91,129,130] [131-138] Gravastars \u0017 ✓ ✓ ∼ [127,139] [140-142] [112,113,135,136,138,142-148] AdS bubbles \u0017 ✓ ∼ \u0017 [149] [149] Wormholes \u0017 ✓ ✓ ∼ [150-153] [154-157] [136,138,148] Fuzzballs \u0017 \u0017 \u0017 ∼ (but see [158-161]) (but see [135,148,162])"}],"limit":50,"offset":0}