Article
Astronomy & Astrophysics
Antonio De Felice, Andreas Doll, Francois Larrouturou, Shinji Mukohyama
Summary: This study investigates spherically symmetric vacuum solutions in the context of the recently proposed type-II minimally modified gravity theory. Despite local differences from the traditional metric, the solutions can be recovered to the standard metric by imposing suitable asymptotic conditions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Cosimo Bambi, Dejan Stojkovic
Summary: Wormholes are hypothetical structures in spacetime with non-trivial topology that challenge the possibility of their existence. This article provides a concise review of past and current efforts to search for astrophysical wormholes in the Universe.
Article
Physics, Particles & Fields
Adrian Ka-Wai Chung, Mairi Sakellariadou
Summary: A method is proposed to constrain the temperature of astrophysical black holes by detecting the inspiral phase of binary black hole coalescences. It is found that inspiraling black holes lose part of their masses during the inspiral phase, leading to faster coalescence and a correction to the orbital phase. Through gravitational wave detection, the temperature of inspiraling black holes is constrained to be less than about 10^(9) K, indicating no evidence for strong quantum-gravity effects during the detection of the inspiral phase.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Ruben Campos Delgado, Sergei V. Ketov
Summary: In this study, we investigate the physical properties of a Schwarzschild-type black hole in the framework of the recently proposed Starobinsky-Bel-Robinson (SBR) modified theory of gravity. We compute the temperature, entropy, pressure, and lifetime of the black hole using perturbation theory in the coupling constant.
Article
Astronomy & Astrophysics
Guillermo Lara, Mario Herrero-Valea, Enrico Barausse, Sergey M. Sibiryakov
Summary: Horava gravity proposes completing general relativity by interactions violating Lorentz invariance at high energies, with solutions showing various geometric properties and uncertainty regarding their formation from gravitational collapse.
Article
Astronomy & Astrophysics
Fabio M. Mele, Johannes Muench, Stratos Pateloudis
Summary: In this paper, the authors continue the analysis of the effective model of quantum Schwarzschild black holes. They find that the central singularity is resolved in the quantum-corrected spacetime and quantum effects become relevant at a mass-independent curvature scale. They focus on the thermodynamic properties of the effective polymer black hole and analyze the quantum corrections as functions of black and white hole masses. The study reveals an extremal minimal-sized configuration characterized by vanishing temperature and entropy. For large masses, the classical results are recovered and quantum corrections are negligible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Brayden Hull, Robert B. Mann
Summary: In this study, the thermodynamics of a new class of asymptotically anti-de Sitter black holes with nonconstant curvature event horizons in Gauss-Bonnet Lovelock gravity are examined, with the cosmological constant acting as thermodynamic pressure. It is found that nontrivial curvature on the horizon can significantly affect their thermodynamic behavior, and novel triple points are observed in six dimensions between large and small uncharged black holes and thermal AdS. For charged black holes, a continuous set of triple points is found, with the range depending on the parameters in the horizon geometry. Additionally, new generalizations of massless and negative mass solutions previously observed in Einstein gravity are also identified.
Article
Astronomy & Astrophysics
Khadije Jafarzade, Mahdi Kord Zangeneh, Francisco S. N. Lobo
Summary: This paper investigates black holes in the consistent Aoki-Gorji-Mukohyama theory of 4D EGB gravity with Born-Infeld nonlinear electrodynamics. It examines optical features such as shadow radius, energy emission rate, and deflection angle, showing that variations in theory parameters have specific effects on optical features of the black hole solution, and this model can be tested through astrophysical observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Ivo Sengo, Pedro V. P. Cunha, Carlos A. R. Herdeiro, Eugen Radu
Summary: We investigate the gravitational lensing by spinning Proca stars and Kerr black holes with Proca hair, discussing their theoretical aspects and observational constraints from EHT data. Theoretical analysis reveals the optical appearance and exotic features of these BHs, interpreted in terms of photon orbit structure. Observationally, the current EHT constraints are compatible with BHs formed from the superradiant instability of Kerr BHs. The resolution of future observations is estimated to better constrain this model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Albert Escriva, Cristiano Germani, Ravi K. Sheth
Summary: The study shows that when the fluid filling the cosmological background is a perfect fluid with w greater than or equal to 1/3, there is a critical threshold for black hole formation that is only related to the curvature of the compaction function. For smaller w values, knowledge of the full shape of the compaction function is necessary.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Indrani Banerjee, Subhadip Sau, Soumitra SenGupta
Summary: With the recent release of the black hole image of Sgr A* alongside the earlier image of M87*, there is hope for a better understanding of gravitational physics at the horizon scale. This paper investigates the regular black hole scenario with a Minkowski core as a possible explanation for the observed shadow of M87* and Sgr A*. The results suggest that the observed shadows favor a regular black hole with a small non-zero charge.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Wei-Hsiang Shao, Che-Yu Chen, Pisin Chen
Summary: Researchers have extended a rotating solution from the minimal Einstein-scalar theory to Eddington-inspired Born-Infeld gravity, parametrizing the new solution. High-energy modifications are able to suppress but not completely remove the curvature divergence of the original naked singularity, and the scalar field induces a peculiar oblateness to the appearance of the shadow.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Guo-Ping Li, Ke-Jian He
Summary: In this paper, the shadows and rings of the KS black hole in deformed HL gravity were carefully investigated using the ray-tracing method. The results show a decrease in certain parameters and an increase in effective potential with an increase in the omega parameter, with direct emissions dominating the total observed intensity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jitendra Kumar, Shafqat Ul Islam, Sushant G. Ghosh
Summary: In this study, a rotating black hole metric is constructed based on the research of LQG black holes, which exhibits rich spacetime structures and differs from Kerr black holes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Shafqat Ul Islam, Jitendra Kumar, Sushant G. Ghosh
Summary: The study focuses on strong field gravitational lensing by rotating Simpson-Visser black holes and distinguishes them quantitatively from Kerr black holes via gravitational lensing effects. The research discusses the astrophysical consequences in supermassive black holes and finds deviations in lensing observables which may not be resolved by current observations but could be determined with future observations. The study also presents a two-dimensional lens equation and formula for deflection angle in the strong field limit.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Phil Uttley, Roland den Hartog, Cosimo Bambi, Didier Barret, Stefano Bianchi, Michal Bursa, Massimo Cappi, Piergiorgio Casella, Webster Cash, Elisa Costantini, Thomas Dauser, Maria Diaz Trigo, Keith Gendreau, Victoria Grinberg, Jan-Willem den Herder, Adam Ingram, Erin Kara, Sera Markoff, Beatriz Mingo, Francesca Panessa, Katja Poppenhaeger, Agata Rozanska, Jiri Svoboda, Ralph Wijers, Richard Willingale, Joern Wilms, Michael Wise
Summary: X-ray interferometry (XRI) is a technique that provides ultra-high spatial resolution for studying various cosmic phenomena at high energies, such as accreting supermassive black holes, X-ray binary systems, and stellar coronae. With a multi-spacecraft interferometer, it is possible to resolve SMBH event horizons in active galaxies and study the dynamics and emission effects of accreting gas close to black holes in detail.
EXPERIMENTAL ASTRONOMY
(2021)
Article
Mathematics
Cosimo Bambi
Summary: Einstein's theory of General Relativity, a pillar of modern physics, has been mainly tested in the weak field regime for decades, but recent years have seen significant progress in testing the theory in the strong field regime with black holes and neutron stars data.
ARABIAN JOURNAL OF MATHEMATICS
(2022)
Article
Astronomy & Astrophysics
Zuobin Zhang, Honghui Liu, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Menglei Zhou
Summary: In this study, the spins of black holes were measured using the continuum-fitting and the iron-line methods, and three NuSTAR observations of the black hole binary GRS 1716-249 were analyzed. The analysis confirmed the Kerr nature of the black hole in GRS 1716-249 and provided stringent constraints on possible deviations from the predictions of general relativity.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Shafqat Riaz, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Haiyang Wang, Zhibo Yu
Summary: This article investigates the impact of a disk-like corona on the measurement of system properties and testing the Kerr nature of a black hole by simulating observations of a black hole binary. The study finds that while the astrophysical properties of the accretion disk can be well recovered, it is more challenging to constrain the geometric properties of the black hole spacetime.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Victoria Grinberg, Honghui Liu, Menglei Zhou
Summary: In this study, the hypothesis of Kerr black hole was tested with a stellar-mass black hole in GRS 1915+105 by analyzing five disk-dominated RXTE spectra and one reflection-dominated Suzaku spectrum. The combination of the constraints from the continuum-fitting and the iron line methods has the potential to provide more stringent tests of the Kerr metric.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Jiachen Jiang, Zuobin Zhang, Cosimo Bambi, Long Ji, Lingda Kong, Shu Zhang
Summary: The low-mass X-ray binary GX 339-4 underwent a new outburst in 2021, during which the flux rapidly alternated between low and high states. Time-resolved spectral analysis revealed that the flux changes occurred primarily in the hard X-ray band. The variability was attributed to the reflected emission from the inner accretion disc and the power-law continuum from the corona.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Yuhan Fu, Cosimo Bambi, Jiachen Jiang, Michael L. Parker, Long Ji, Lingda Kong, Liang Zhang, Shu Zhang, Yuexin Zhang
Summary: We analyzed three observations of GRS 1915+105 in 2017 and found strong absorption lines from highly ionized iron in the disk wind outflowing at a velocity of about 1000 km/s. Two of the observations showed significant oscillations in their light curves, corresponding to the kappa state of GRS 1915+105. The variation in the ionization state of the disk wind follows the X-ray continuum on timescales ranging from hundreds of seconds to months, with the wind's radial location consistent with thermal driving. The mass-loss rate due to the outflowing wind is comparable to the mass accretion rate in the inner disk, indicating the important role of the disk wind in the accretion system.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Swarnim Shashank, Shafqat Riaz, Askar B. Abdikamalov, Cosimo Bambi
Summary: X-ray reflection spectroscopy is a leading technique for studying black hole accretion disks, but its accuracy relies on the reflection models used. This study uses a general relativistic magnetohydrodynamic code and ray-tracing techniques to test the capability of current reflection models in recovering the correct input parameters.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Cosimo Bambi, Jiachen Jiang, Javier A. Garcia, Long Ji, Lingda Kong, Xiaoqin Ren, Shu Zhang, Shuangnan Zhang
Summary: We analyze the relativistic reflection spectra of GX 339-4 during its 2021 outburst and find strong relativistic reflection signatures indicating a high black hole spin and an intermediate disk inclination angle. The hard-to-soft transition is accompanied by an increasing disk temperature and a softening corona emission, while the inner disk radius remains stable. The corona height, assuming a lamppost geometry, stays close to the black hole across the state transition. Including Comptonization, the scattering fraction parameter decreases during the transition. Our analysis with a reflection model designed for hot accretion disks supports the scenario of corona property variations during the state transition.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Zuobin Zhang, Jiachen Jiang, Honghui Liu, Cosimo Bambi, Christopher S. Reynolds, Andrew C. Fabian, Thomas Dauser, Kristin Madsen, Andrew Young, Luigi Gallo, Zhibo Yu, John Tomsick
Summary: We present the results from a joint XMM-Newton + NuSTAR observation of the Seyfert 1 galaxy ESO 511-G030, showing that the source remained in a low flux and stable state. The broadband spectrum indicates the presence of a power-law continuum, a soft excess below 2 keV, a narrow iron Ka emission, and a high-energy cutoff. Two possible scenarios, a warm and optically thick Comptonizing corona or a relativistic reflection from a high-density inner disk, can explain the observed soft excess. All models require a low temperature for the hot corona.
ASTROPHYSICAL JOURNAL
(2023)
Review
Multidisciplinary Sciences
Cosimo Bambi
Summary: General relativity, one of the pillars of modern physics, has been predominantly tested in the weak-field regime until recently. However, advances in observational facilities have allowed for exploration of the strong-field regime, providing data for gravitational wave tests, black hole imaging, and X-ray tests of general relativity. This manuscript aims to provide a pedagogical review on X-ray tests of general relativity with black holes and compare them with gravitational wave tests and black hole imaging.
Article
Astronomy & Astrophysics
Honghui Liu, Jiachen Jiang, Zuobin Zhang, Cosimo Bambi, Andrew C. Fabian, Javier A. Garcia, Adam Ingram, Erin Kara, James F. Steiner, John A. Tomsick, Dominic J. Walton, Andrew J. Young
Summary: We conducted a high-density relativistic reflection analysis on 21 spectra of six black hole X-ray binaries in the hard state using data from NuSTAR and Swift. Our findings indicate that 76% of the observations in our sample require a disk density higher than the previously assumed 10^15 cm(-3) in reflection analysis. Stellar mass black holes have higher disk densities compared to active galactic nuclei. Our results suggest that the inner disk radius is close to the innermost stable circular orbit in the luminous hard state, and the coronal temperatures are lower than expected, which can be explained by a hybrid plasma model. The disk ionization parameter is overestimated when assuming a fixed density of 10^15 cm(-3), while the inner disk radius remains unaffected.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Q. Yuan, Pankaj Kushwaha, Alok C. Gupta, Ashutosh Tripathi, Paul J. Wiita, M. Zhang, X. Liu, Anne Lahteenmaki, Merja Tornikoski, Joni Tammi, Venkatessh Ramakrishnan, L. Cui, X. Wang, M. F. Gu, Cosimo Bambi, A. E. Volvach
Summary: In this study, correlation and periodicity analyses were performed on the multiband light curves of PKS 1510-089, a flat-spectrum radio quasar. The results show correlations between gamma-ray, optical, and near-infrared emissions with no time lags, while both gamma-ray and optical/near-infrared emissions precede radio radiation. Furthermore, evidence for a quasi-periodic variation of approximately 1540 days was found in the 37 GHz light curve, suggesting periodic behaviors in the unresolved core emission. The color variability analysis reveals that the source follows a redder-when-brighter trend over time, even in the low-flux state.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Swarnim Shashank, Cosimo Bambi
Summary: Gravitational-wave observations of binary black holes were used to test the Kerr hypothesis, and the results showed consistency.
Article
Astronomy & Astrophysics
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Victoria Grinberg, Menglei Zhou
Summary: The simultaneous observations of the black hole binary GX 339-4 with NuSTAR and Swift revealed strong thermal components and prominent relativistic reflection features. Precise measurements of the Johannsen deformation parameter alpha(13) were obtained at a 90% confidence level, investigating systematic uncertainties by fitting data with different models.
ASTROPHYSICAL JOURNAL
(2021)