Galactic Center Shadows: Beyond the Standard Model A. F. Zakharov Physics of Atomic Nuclei, 2025 In 2005 Zakharov et al. predicted an opportunity to reconstruct a shadow in Sgr A* with ground based or space—ground interferometer acting in mm or sub-mm band (the Millimetron was mentioned for such needs). The prediction was confirmed in May 2022 since the Event Horizon Telescope (EHT) Collaboration presented results of a shadow reconstruction for our Galactic Center (the shadow around the supermassive black hole in M87 was reconstructed in 2019). These reconstructions were based on EHT observations done in 2017. In 2005 Zakharov et al. also derived analytical expressions for shadow size as a function of charge for Reissner–Nordström metric and later these results were generalized for a tidal charge case. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow size estimates done by the EHT Collaboration, in particular, a tidal charge could be estimated from these observations. We also discuss opportunities to use Millimetron facilities for shadow reconstructions in M87* and Sgr A*. In our recent studies we discuss shadow formations for cases where naked singularities, wormholes or more exotic models substitute conventional black holes in galactic centers.
Astrophysical Tests of General Relativity A. F. Zakharov Physics of Particles and Nuclei, 2024 At the initial stage of its development, general relativity (GR) was verified and confirmed in a weak gravitational field limit. However, with the development of astronomical observation technologies, GR predictions in a strong gravitational field began to be discussed and confirmed, such as the profile of the X-ray iron $$K\\alpha $$ line (in the case if the emission region is very close to the event horizon), the trajectories of stars near black holes and the shapes and sizes of shadows of supermassive black holes in M87* and Sgr A*. In 2005 it was predicted that a shadow formed near a supermassive black hole at the Galactic Center could be reconstructed from observations of ground based global VLBI system or ground—space interferometer acting in mm or sub-mm bands. In 2022 this prediction was confirmed since the Event Horizon Telescope (EHT) collaboration reported about a shadow reconstructions for Sgr A*. In 2019 the EHT collaboration presented the first image reconstruction around the shadow for the supermassive black hole in M87. In 2021 the EHT collaboration constrained parameters (“charges”) of spherical symmetrical metrics of black holes from an allowed interval for shadow radius. In 2022 the EHT collaboration constrained charges of metrics for the supermassive black hole at the Galactic Center. Earlier, we obtained analytical expressions for the shadow radius as a function of charge (including a tidal one) in the case of Reissner–Nordström metric. Based on results of the shadow size evaluation for M87* done by the EHT collaboration we constrained a tidal charge. We discussed opportunities to use shadows to test alternative theories of gravity and alternative models for galactic centers.
New tests of general relativity Alexander Zakharov Proceedings of Science, 2024 General relativity (GR) was tested in many experiments and observations and always its predictions were confirmed. However, in a majority of tests GR was checked and confirmed in a weak gravitational field regime. In 2005 it was predicted that a shadow formed near a supermassive black hole at the Galactic Center could be reconstructed from observations of ground based global VLBI system or ground – space interferometer acting in mm or sub-mm bands. In 2022 the Event Horizon Telescope (EHT) collaboration reconstructed the shadow for the black hole at the Galactic Center (GC), therefore our prediction was confirmed. In 2019 the EHT collaboration presented the first image reconstruction around the shadow for the supermassive black hole in M87*. In 2021 the EHT collaboration constrained parameters (“charges”) of spherical symmetrical metrics of black holes from an allowed interval for shadow radius. Earlier, we obtained analytical expressions for the shadow radius as a function of charge (including a tidal one) in the case of Reissner–Nordström metric. Based on results of the shadow size evaluation for M87* done by the EHT team we constrain a tidal charge. Similarly we constrained a tidal charge for the black hole at the Galactic Center based on shadow reconstruction done by the EHT collaboration in 2022. We discussed opportunities to use shadows to test alternative theories of gravity and alternative theories for galactic centers. We used also observational data for trajectories of bright stars near the Galactic Center to test gravity theories and theoretical models for the Galactic Center.
Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center Predrag Jovanović, Vesna Borka Jovanović, Duško Borka, Alexander F. Zakharov Symmetry, 2024 In this paper we use a modification of the Newtonian gravitational potential with a non-linear Yukawa-like correction, as it was proposed by C. Will earlier to obtain new bounds on graviton mass from the observed orbits of S-stars around the Galactic Center (GC). This phenomenological potential differs from the gravitational potential obtained in the weak field limit of Yukawa gravity, which we used in our previous studies. We also assumed that the orbital precession of S-stars is close to the prediction of General Relativity (GR) for Schwarzschild precession, but with a possible small discrepancy from it. This assumption is motivated by the fact that the GRAVITY Collaboration in 2020 and in 2022 detected Schwarzschild precession in the S2 star orbit around the Supermassive Black Hole (SMBH) at the GC. Using this approach, we were able to constrain parameter λ of the potential and, assuming that it represents the graviton Compton wavelength, we also found the corresponding upper bound of graviton mass. The obtained results were then compared with our previous estimates, as well as with the estimates of other authors.
Improvement of graviton mass constraints using GRAVITY's detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center Predrag Jovanović, Vesna Borka Jovanović, Duško Borka, Alexander F. Zakharov Physical Review D, 2024 Here we study possible improvements of the existing constraints on the upper bound of graviton mass by the analysis of the stellar orbits around the SMBH at the GC in the framework of Yukawa gravity. A motivation for this study is a recent detection of Schwarzschild precession in the orbit of S2 star around the SMBH at the GC by the GRAVITY Collaboration. The authors indicated that the orbital precession of the S2 star is close to the General Relativity (GR) prediction, but with possible small deviation from it, and parametrized this effect by introducing an ad hoc factor in the parametrized PPN equations of motion. Here we use the value of this factor presented by GRAVITY in order to perform two-body simulations of the stellar orbits in massive gravity using equations of motion in the modified PPN formalism, as well as to constrain the range of massive interaction $\\Lambda$. From the obtained values of $\\Lambda$, and assuming that it corresponds to the Compton wavelength of graviton, we then calculated new estimates for the upper bound of graviton mass which are found to be independent, but consistent with the LIGO's estimate of graviton mass from the first GW signal GW150914 (later this graviton mass estimation was significantly improved with consequent observations of GW events). We also performed calculations including numerical simulations in order to constrain the bounds on graviton mass in the case of a small deviation of the stellar orbits from the corresponding GR predictions and showed that our method could further improve previous estimates for upper bounds on the graviton mass. It is also demonstrated that such analysis of the observed orbits of S-stars around the GC in the frame of the Yukawa gravity represents a tool for constraining the upper bound for the graviton mass, as well as for probing the predictions of GR or other gravity theories.
Constraints on graviton mass and a tidal charge with observations of the galactic center Proceedings of the 54th Rencontres De Moriond 2019 Gravitation, 2019
Gravitational lensing properties of cosmological black holes A. F. Zakharov, S. Capozziello, C. Stornaiolo 14th Marcel Grossman Meeting on Recent Developments in Theoretical and Experimental General Relativity Astrophysics and Relativistic Field Theories Proceedings, 2018
S2 like star orbits near the Galactic Center in Rn and Yukawa gravity Advances in General Relativity Research, 2015
Polarization profiles for selected microlensing events towards the galactic bulge A.A NUCITA, G. INGROSSO, F. DE PAOLIS, F. STRAFELLA, S. CALCHI-NOVATI, et al. 13th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity Astrophysics and Relativistic Field Theories Proceedings of the Mg13 Meeting on General Relativity 2012, 2015
Orbits of S2 star in Yukawa gravity: Simulations vs observations 8th Mathematical Physics Meeting Summer School and Conference on Modern Mathematical Physics Mphys 2014, 2014
Theoretical estimations of future polarization observations for exoplanery searches with gravitational microlensing Proceedings of Science, 2014
Origin of masses in the Early Universe Proceedings of Science, 2014
Observational signatures for reissner-nordström black hole with significant charge at the galactic center 7th Mathematical Physics Meeting Summer School and Conference on Modern Mathematical Physics 2012 Mphys 2012, 2012
Orbital precession in Rn gravity: Simulations vs observations (the S2 star orbit case) 7th Mathematical Physics Meeting Summer School and Conference on Modern Mathematical Physics 2012 Mphys 2012, 2012
Detection of exoplanets in M31 with pixel-lensing: The event PA-99-N2 case G. INGROSSO, F. DE PAOLIS, S. CALCHI NOVATI, PH. JETZER, A. A. NUCITA, et al. 12th Marcel Grossmann Meeting on Recent Dev in Theoretical and Experimental General Relativity Astrophysics and Relativistic Field Theories Proc of the mg 2009 Meeting on General Relativity, 2012
Constraints on a model with extra dimensions for the black hole at the Galactic Center Proceedings of the 46th Rencontres De Moriond and Gphys Colloquium 2011 Gravitational Waves and Experimental Gravity, 2011
Conformal Hamiltonian dynamics of general relativity A.B. Arbuzov, B.M. Barbashov, R.G. Nazmitdinov, V.N. Pervushin, A. Borowiec, et al. Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, 2010
Relativistic trajectories of celestial bodies as a tool to constrain f(r) theories of gravity and dark matter concentration near the galactic center Proceedings of the 45th Rencontres De Moriond on Cosmology 2010, 2010
Exoplanet searches with gravitational microlensing Proceedings of the 6th Mathematical Physics Meeting Summer School and Conference on Modern Mathematical Physics, 2010
Microlensing with the radioastron space telescope ALEXANDER F. ZAKHAROV 11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity Gravitation and Relativistic Field Theories Proc of the Mg11 Meeting on General Relativity, 2008
Astrometrical microlensing with radioastron ALEXANDER F. ZAKHAROV 11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity Gravitation and Relativistic Field Theories Proc of the Mg11 Meeting on General Relativity, 2008
Solar system constraints on Rn gravity A. F. Zakharov, A. A. Nucita, F. De Paolis, G. Ingrosso Physical Review D Particles Fields Gravitation and Cosmology, 2006
Hamiltonian cosmological perturbation theory B.M. Barbashov, V.N. Pervushin, A.F. Zakharov, V.A. Zinchuk Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, 2006
Microlensing with the radioastron space telescope A. F. Zakharov Proceedings of the 12th Lomonosov Conference on Elementary Particle Physics Particle Physics at the Year of 250th Anniversary of Moscow University, 2006
Are Galactic Clusters Hypermassive Spherically Symmetric Black Holes? AF Zakharov Physics of Particles and Nuclei Letters 23 (1), 87-91 , 2026 2026
KOMMENTARIY K STAT'E SO ALEKSEEVA I DR.«NELOKAL'NYE GRAVITATsIONNYE TEORII I IZOBRAZhENIYa TENEY ChERNYKh DYR», ZhETF 165, 508 (2024) AF Zakharov Žurnal èksperimentalʹnoj i teoretičeskoj fiziki 167 (2), 220-223 , 2025 2025 Citations: 1
Nearly forgotten results in development of physical cosmology AF Zakharov arXiv preprint arXiv:2511.06018 , 2025 2025 Citations: 3
Shadow in the Galactic Center: Theoretical Concept--Prediction--Realization AF Zakharov arXiv preprint arXiv:2506.16927 , 2025 2025 Citations: 3
Shadows and circular photon orbits: Consideration of some cases of generalizations of Kerr–Newman black holes AF Zakharov Physics of Particles and Nuclei Letters 22 (3), 568-575 , 2025 2025 Citations: 1
Shadows of galactic centers: from supermassive black holes to naked singularities and wormholes AF Zakharov Physics of Particles and Nuclei 56 (2), 140-145 , 2025 2025 Citations: 4
Galactic center shadows: Beyond the standard model AF Zakharov Physics of Atomic Nuclei 88 (1), 154-170 , 2025 2025 Citations: 4
Black hole shadows as new tests of General Relativity AF Zakharov Moscow University Physics Bulletin 79 (Suppl 1), 334-343 , 2024 2024 Citations: 6
Astrophysical tests of general relativity AF Zakharov Physics of Particles and Nuclei 55 (6), 1413-1419 , 2024 2024 Citations: 5
Shadows near supermassive black holes: From a theoretical concept to GR test AF Zakharov International Journal of Modern Physics D 33 (14), 2340004 , 2024 2024 Citations: 19
Comment on the article" Non-local gravitational corrections in black hole shadow images" by SO Alexeyev et al AF Zakharov arXiv preprint arXiv:2410.11898 , 2024 2024
Neutron stars and black holes as natural laboratories of fundamental physics AF Zakharov Physics of Particles and Nuclei 55 (4), 716-724 , 2024 2024 Citations: 7
Constraints on graviton mass from Schwarzschild precession in the orbits of S-Stars around the Galactic Center P Jovanović, V Borka Jovanović, D Borka, AF Zakharov Symmetry 16 (4), 397 , 2024 2024 Citations: 11
Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center P Jovanović, V Borka Jovanović, D Borka, AF Zakharov Physical Review D 109 (6), 064046 , 2024 2024 Citations: 20
Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center. Symmetry 2024, 16, 397 P Jovanovic, V Borka Jovanovic, D Borka, AF Zakharov 2024
Trajectories of bright stars and shadows around supermassive black holes as tests of gravity theories AF Zakharov Physics of Particles and Nuclei 54 (5), 889-895 , 2023 2023 Citations: 9
The Galactic center and M87*: Observations and interpretations AF Zakharov Physics of Particles and Nuclei Letters 20 (3), 538-543 , 2023 2023 Citations: 9
Constraints on black hole charges in M87* and Sgr A* with the EHT observations AF Zakharov arXiv preprint arXiv:2305.15446 , 2023 2023 Citations: 5
Constraints on Yukawa gravity parameters from observations of bright stars P Jovanović, V Borka Jovanović, D Borka, AF Zakharov Journal of Cosmology and Astroparticle Physics 2023 (03), 056 , 2023 2023 Citations: 28
Shadows around Sgr A* and M87* as a tool to test gravity theories AF Zakharov arXiv preprint arXiv:2208.06805 , 2022 2022 Citations: 16
MOST CITED SCHOLAR PUBLICATIONS
Constraints on a charge in the Reissner-Nordström metric for the black hole at the Galactic Center AF Zakharov PHYSICAL REVIEW D 90, 062007 (2014) 90, 062007 , 2014 2014 Citations: 214
Microlensing by noncompact objects AF Zakharov, MV Sazhin Journal of Experimental and Theoretical Physics Letters 63 (12), 937-943 , 1996 1996 Citations: 180
Direct measurements of black hole charge with future astrometrical missions AF Zakharov, F De Paolis, G Ingrosso, AA Nucita Astronomy & Astrophysics 442 (3), 795-799 , 2005 2005 Citations: 160
Measuring the black hole parameters in the galactic center with RADIOASTRON AF Zakharov, AA Nucita, F DePaolis, G Ingrosso New Astronomy 10 (6), 479-489 , 2005 2005 Citations: 157
Constraining the range of Yukawa gravity interaction from S2 star orbits D Borka, P Jovanović, VB Jovanović, AF Zakharov Journal of Cosmology and Astroparticle Physics 2013 (11), 050-050 , 2013 2013 Citations: 133
Solar system constraints on gravity AF Zakharov, AA Nucita, F De Paolis, G Ingrosso Physical Review D—Particles, Fields, Gravitation, and Cosmology 74 (10), 107101 , 2006 2006 Citations: 129
Constraints on gravity from precession of orbits of S2-like stars D Borka, P Jovanović, VB Jovanović, AF Zakharov Physical Review D—Particles, Fields, Gravitation, and Cosmology 85 (12), 124004 , 2012 2012 Citations: 113
On the hotspot near a Kerr black hole: Monte-Carlo simulations AF Zakharov Monthly Notices of the Royal Astronomical Society 269 (2), 283-288 , 1994 1994 Citations: 107
Gravitational lenses and microlenses AF Zakharov Yanus-K, Moscow , 1997 1997 Citations: 105
Apoastron shift constraints on dark matter distribution at the Galactic Center AF Zakharov, AA Nucita, F De Paolis, G Ingrosso Physical Review D—Particles, Fields, Gravitation, and Cosmology 76 (6), 062001 , 2007 2007 Citations: 104
Constraining the range of Yukawa gravity interaction from S2 star orbits II: bounds on graviton mass AF Zakharov, P Jovanović, D Borka, VB Jovanović Journal of Cosmology and Astroparticle Physics 2016 (05), 045-045 , 2016 2016 Citations: 99
Shadows as a tool to evaluate black hole parameters and a dimension of spacetime AF Zakharov, F De Paolis, G Ingrosso, AA Nucita New Astronomy Reviews 56 (2-3), 64-73 , 2012 2012 Citations: 92
On the magnification of gravitational lens images near cusps. AF Zakharov Astronomy and Astrophysics, Vol. 293, p. 1-4 (1995) 293, 1-4 , 1995 1995 Citations: 88
A Study of the Correlation between the Amplification of the Fe Kα Line and the X-Ray Continuum of Quasars due to Microlensing LČ Popović, P Jovanović, E Mediavilla, AF Zakharov, C Abajas, JA Munoz, ... The Astrophysical Journal 637 (2), 620-630 , 2006 2006 Citations: 85
Pixel lensing as a way to detect extrasolar planets in M31 G Ingrosso, SC Novati, F De Paolis, P Jetzer, AA Nucita, AF Zakharov Monthly Notices of the Royal Astronomical Society 399 (1), 219-228 , 2009 2009 Citations: 84
Magnetic fields in active galactic nuclei and microquasars AF Zakharov, NS Kardashev, VN Lukash, SV Repin Monthly Notices of the Royal Astronomical Society 342 (4), 1325-1333 , 2003 2003 Citations: 83
Particle capture cross sections for a Reissner--Nordström black hole AF Zakharov Classical and Quantum Gravity 11 (4), 1027-1033 , 1994 1994 Citations: 76
Constraints on tidal charge of the supermassive black hole at the Galactic Center with trajectories of bright stars AF Zakharov The European Physical Journal C 78 (8), 689 , 2018 2018 Citations: 75
Sgr A*: A laboratory to measure the central black hole and stellar cluster parameters AA Nucita, F De Paolis, G Ingrosso, A Qadir, AF Zakharov Publications of the Astronomical Society of the Pacific 119 (854), 349-359 , 2007 2007 Citations: 73
Constraints on Rn gravity from precession of orbits of S2-like stars: A case of a bulk distribution of mass AF Zakharov, D Borka, VB Jovanović, P Jovanović Advances in Space Research 54 (6), 1108-1112 , 2014 2014 Citations: 66
