TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Zakharov, Alexander F.
PY  - 2024
PY  - 4
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/13141
AB  - 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.
T2  - Symmetry
T1  - Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center
VL  - 16
VL  - 16
IS  - 4
SP  - 397
SP  - 387
DO  - 10.3390/sym16040397
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Zakharov, Alexander F.",
year = "2024, 4",
abstract = "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.",
journal = "Symmetry",
title = "Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center",
volume = "16, 16",
number = "4",
pages = "397-387",
doi = "10.3390/sym16040397"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Zakharov, A. F.. (2024). Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center. in Symmetry, 16(4), 397.
https://doi.org/10.3390/sym16040397

Jovanović P, Borka Jovanović V, Borka D, Zakharov AF. Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center. in Symmetry. 2024;16(4):397.
doi:10.3390/sym16040397 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Zakharov, Alexander F., "Constraints on Graviton Mass from Schwarzschild Precession in the Orbits of S-Stars around the Galactic Center" in Symmetry, 16, no. 4 (2024):397,
https://doi.org/10.3390/sym16040397 . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Zakharov, Alexander F.
PY  - 2024
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/13024
AB  - Here we study possible improvements of the existing constraints on the upper bound of the graviton mass by the analysis of the stellar orbits around the supermassive black hole (SMBH) at the Galactic Center (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 post-Newtonian (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 Λ. From the obtained values of Λ, 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 gravitational wave (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 the upper bounds on the graviton mass. It is also demonstrated that such an 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.
T2  - Physical Review D
T1  - Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center
VL  - 109
IS  - 6
SP  - 064046
DO  - 10.1103/PhysRevD.109.064046
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Zakharov, Alexander F.",
year = "2024",
abstract = "Here we study possible improvements of the existing constraints on the upper bound of the graviton mass by the analysis of the stellar orbits around the supermassive black hole (SMBH) at the Galactic Center (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 post-Newtonian (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 Λ. From the obtained values of Λ, 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 gravitational wave (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 the upper bounds on the graviton mass. It is also demonstrated that such an 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.",
journal = "Physical Review D",
title = "Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center",
volume = "109",
number = "6",
pages = "064046",
doi = "10.1103/PhysRevD.109.064046"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Zakharov, A. F.. (2024). Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center. in Physical Review D, 109(6), 064046.
https://doi.org/10.1103/PhysRevD.109.064046

Jovanović P, Borka Jovanović V, Borka D, Zakharov AF. Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center. in Physical Review D. 2024;109(6):064046.
doi:10.1103/PhysRevD.109.064046 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Zakharov, Alexander F., "Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center" in Physical Review D, 109, no. 6 (2024):064046,
https://doi.org/10.1103/PhysRevD.109.064046 . .

TY  - JOUR
AU  - Lazarov, Nenad Đ.
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/11234
AB  - In our work we presented the modified field equations generated by action with unspecified function f (R). Assuming spherical symmetry, we used the corresponding static Schwarzschild-like metric in the weak field limit. Also we considered geodesic equations of motion describing orbits and orbital speeds which can be measured in galactic environment. We solved geodesic equations in the case of a power-law f (R) theories, that is we set f (R) = f0nRn.
T2  - Filomat
T1  - Geodesic equations in the weak field limit of general f (R) gravity theory
VL  - 37
IS  - 25
SP  - 8575
EP  - 8581
DO  - 10.2298/FIL2325575L
ER  - 

@article{
author = "Lazarov, Nenad Đ. and Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "In our work we presented the modified field equations generated by action with unspecified function f (R). Assuming spherical symmetry, we used the corresponding static Schwarzschild-like metric in the weak field limit. Also we considered geodesic equations of motion describing orbits and orbital speeds which can be measured in galactic environment. We solved geodesic equations in the case of a power-law f (R) theories, that is we set f (R) = f0nRn.",
journal = "Filomat",
title = "Geodesic equations in the weak field limit of general f (R) gravity theory",
volume = "37",
number = "25",
pages = "8575-8581",
doi = "10.2298/FIL2325575L"
}

Lazarov, N. Đ., Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Geodesic equations in the weak field limit of general f (R) gravity theory. in Filomat, 37(25), 8575-8581.
https://doi.org/10.2298/FIL2325575L

Lazarov NĐ, Borka Jovanović V, Borka D, Jovanović P. Geodesic equations in the weak field limit of general f (R) gravity theory. in Filomat. 2023;37(25):8575-8581.
doi:10.2298/FIL2325575L .

Lazarov, Nenad Đ., Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Geodesic equations in the weak field limit of general f (R) gravity theory" in Filomat, 37, no. 25 (2023):8575-8581,
https://doi.org/10.2298/FIL2325575L . .

TY  - JOUR
AU  - Borka-Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/12725
AB  - Here we investigate the giant radio galaxy DA 240, which is a FR II source. Specifically, we investigate its flux density, as well as the spectral index distribution. For that purpose, we used publicly available data for the source: Leahy's atlas of double radio-sources and NASA/IPAC Extragalactic Database (NED). We used observations at 326 MHz (92 cm) and at 608 MHz (49 cm) and obtained spectral index distributions between 326 and 608 MHz. For the first time we give spectral index map for these frequencies. We found that the synchrotron radiation is the dominant radiation mechanism over most of the area of DA 240, and also investigated the mechanism of radiation at some characteristic points, namely its core and the hotspots. The results of this study will be helpful for understanding the evolutionary process of the DA 240 radio source.
T2  - Contributions of the Astronomical Observatory Skalnaté Pleso
T1  - Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240
VL  - 53
IS  - 3
SP  - 188
EP  - 196
DO  - 10.31577/caosp.2023.53.3.188
ER  - 

@article{
author = "Borka-Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "Here we investigate the giant radio galaxy DA 240, which is a FR II source. Specifically, we investigate its flux density, as well as the spectral index distribution. For that purpose, we used publicly available data for the source: Leahy's atlas of double radio-sources and NASA/IPAC Extragalactic Database (NED). We used observations at 326 MHz (92 cm) and at 608 MHz (49 cm) and obtained spectral index distributions between 326 and 608 MHz. For the first time we give spectral index map for these frequencies. We found that the synchrotron radiation is the dominant radiation mechanism over most of the area of DA 240, and also investigated the mechanism of radiation at some characteristic points, namely its core and the hotspots. The results of this study will be helpful for understanding the evolutionary process of the DA 240 radio source.",
journal = "Contributions of the Astronomical Observatory Skalnaté Pleso",
title = "Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240",
volume = "53",
number = "3",
pages = "188-196",
doi = "10.31577/caosp.2023.53.3.188"
}

Borka-Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240. in Contributions of the Astronomical Observatory Skalnaté Pleso, 53(3), 188-196.
https://doi.org/10.31577/caosp.2023.53.3.188

Borka-Jovanović V, Borka D, Jovanović P. Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240. in Contributions of the Astronomical Observatory Skalnaté Pleso. 2023;53(3):188-196.
doi:10.31577/caosp.2023.53.3.188 .

Borka-Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240" in Contributions of the Astronomical Observatory Skalnaté Pleso, 53, no. 3 (2023):188-196,
https://doi.org/10.31577/caosp.2023.53.3.188 . .

TY  - CONF
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/11941
AB  - Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.
C3  - Proceedings of Science
T1  - Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84
VL  - 427
SP  - 193246
DO  - 10.22323/1.427.0043
ER  - 

@conference{
author = "Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.",
journal = "Proceedings of Science",
title = "Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84",
volume = "427",
pages = "193246",
doi = "10.22323/1.427.0043"
}

Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84. in Proceedings of Science, 427, 193246.
https://doi.org/10.22323/1.427.0043

Borka Jovanović V, Borka D, Jovanović P. Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84. in Proceedings of Science. 2023;427:193246.
doi:10.22323/1.427.0043 .

Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84" in Proceedings of Science, 427 (2023):193246,
https://doi.org/10.22323/1.427.0043 . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Zakharov, Alexander F.
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10849
AB  - In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction Λ and universal constant δ) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction [1]. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant δ, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction δ and find that this parameter has strong influence on range of Yukawa interaction Λ. For that purpose we use parameterized post-Newtonian (PPN) equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.
T2  - Journal of Cosmology and Astroparticle Physics
T1  - Constraints on Yukawa gravity parameters from observations of bright stars
IS  - 03
SP  - 056
DO  - 10.1088/1475-7516/2023/03/056
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Zakharov, Alexander F.",
year = "2023",
abstract = "In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction Λ and universal constant δ) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction [1]. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant δ, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction δ and find that this parameter has strong influence on range of Yukawa interaction Λ. For that purpose we use parameterized post-Newtonian (PPN) equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.",
journal = "Journal of Cosmology and Astroparticle Physics",
title = "Constraints on Yukawa gravity parameters from observations of bright stars",
number = "03",
pages = "056",
doi = "10.1088/1475-7516/2023/03/056"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Zakharov, A. F.. (2023). Constraints on Yukawa gravity parameters from observations of bright stars. in Journal of Cosmology and Astroparticle Physics(03), 056.
https://doi.org/10.1088/1475-7516/2023/03/056

Jovanović P, Borka Jovanović V, Borka D, Zakharov AF. Constraints on Yukawa gravity parameters from observations of bright stars. in Journal of Cosmology and Astroparticle Physics. 2023;(03):056.
doi:10.1088/1475-7516/2023/03/056 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Zakharov, Alexander F., "Constraints on Yukawa gravity parameters from observations of bright stars" in Journal of Cosmology and Astroparticle Physics, no. 03 (2023):056,
https://doi.org/10.1088/1475-7516/2023/03/056 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Nikolić, Violeta N.
AU  - Lazarov, Nenad Đ.
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10151
AB  - We estimate the parameters of the Hybrid Palatini gravity model with the Schwarzschild precession of S-stars, specifically of the S2, S38 and S55 stars. We also take into account the case of bulk mass distribution near the Galactic Center. We assume that the Schwarzschild orbital precession of mentioned S-stars is the same as in General Relativity (GR) in all studied cases. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. The astronomical data analysis of S38 and S55 orbits showed that, also in these cases, the orbital precession is close to the GR prediction. Based on this observational fact, we evaluated the parameters of the Hybrid Palatini Gravity model with the Schwarzschild precession of the S2, S38 and S55 stars, and we estimated the range of parameters of the Hybrid Palatini gravity model for which the orbital precession is as in GR for all three stars. We also evaluated the parameters of the Hybrid Palatini Gravity model in the case of different values of bulk mass density distribution of extended matter. We believe that proposed method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
T2  - Universe
T1  - Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution
VL  - 8
IS  - 2
SP  - 70
DO  - 10.3390/universe8020070
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Nikolić, Violeta N. and Lazarov, Nenad Đ. and Jovanović, Predrag",
year = "2022",
abstract = "We estimate the parameters of the Hybrid Palatini gravity model with the Schwarzschild precession of S-stars, specifically of the S2, S38 and S55 stars. We also take into account the case of bulk mass distribution near the Galactic Center. We assume that the Schwarzschild orbital precession of mentioned S-stars is the same as in General Relativity (GR) in all studied cases. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. The astronomical data analysis of S38 and S55 orbits showed that, also in these cases, the orbital precession is close to the GR prediction. Based on this observational fact, we evaluated the parameters of the Hybrid Palatini Gravity model with the Schwarzschild precession of the S2, S38 and S55 stars, and we estimated the range of parameters of the Hybrid Palatini gravity model for which the orbital precession is as in GR for all three stars. We also evaluated the parameters of the Hybrid Palatini Gravity model in the case of different values of bulk mass density distribution of extended matter. We believe that proposed method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.",
journal = "Universe",
title = "Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution",
volume = "8",
number = "2",
pages = "70",
doi = "10.3390/universe8020070"
}

Borka, D., Borka Jovanović, V., Nikolić, V. N., Lazarov, N. Đ.,& Jovanović, P.. (2022). Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution. in Universe, 8(2), 70.
https://doi.org/10.3390/universe8020070

Borka D, Borka Jovanović V, Nikolić VN, Lazarov NĐ, Jovanović P. Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution. in Universe. 2022;8(2):70.
doi:10.3390/universe8020070 .

Borka, Duško, Borka Jovanović, Vesna, Nikolić, Violeta N., Lazarov, Nenad Đ., Jovanović, Predrag, "Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution" in Universe, 8, no. 2 (2022):70,
https://doi.org/10.3390/universe8020070 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Capozziello, Salvatore
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10420
AB  - We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.
T2  - Advances in Space Research
T1  - Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model
VL  - 71
IS  - 2
SP  - 1235
EP  - 1244
DO  - 10.1016/j.asr.2022.08.060
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Capozziello, Salvatore and Jovanović, Predrag",
year = "2022",
abstract = "We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.",
journal = "Advances in Space Research",
title = "Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model",
volume = "71",
number = "2",
pages = "1235-1244",
doi = "10.1016/j.asr.2022.08.060"
}

Borka, D., Borka Jovanović, V., Capozziello, S.,& Jovanović, P.. (2022). Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model. in Advances in Space Research, 71(2), 1235-1244.
https://doi.org/10.1016/j.asr.2022.08.060

Borka D, Borka Jovanović V, Capozziello S, Jovanović P. Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model. in Advances in Space Research. 2022;71(2):1235-1244.
doi:10.1016/j.asr.2022.08.060 .

Borka, Duško, Borka Jovanović, Vesna, Capozziello, Salvatore, Jovanović, Predrag, "Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model" in Advances in Space Research, 71, no. 2 (2022):1235-1244,
https://doi.org/10.1016/j.asr.2022.08.060 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Arsenić, Arsenije
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10341
AB  - The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy’s Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN.
T2  - Advances in Space Research
T1  - Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format
DO  - 10.1016/j.asr.2022.05.062
ER  - 

@article{
author = "Borka Jovanović, Vesna and Borka, Duško and Arsenić, Arsenije and Jovanović, Predrag",
year = "2022",
abstract = "The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy’s Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN.",
journal = "Advances in Space Research",
title = "Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format",
doi = "10.1016/j.asr.2022.05.062"
}

Borka Jovanović, V., Borka, D., Arsenić, A.,& Jovanović, P.. (2022). Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format. in Advances in Space Research.
https://doi.org/10.1016/j.asr.2022.05.062

Borka Jovanović V, Borka D, Arsenić A, Jovanović P. Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format. in Advances in Space Research. 2022;.
doi:10.1016/j.asr.2022.05.062 .

Borka Jovanović, Vesna, Borka, Duško, Arsenić, Arsenije, Jovanović, Predrag, "Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format" in Advances in Space Research (2022),
https://doi.org/10.1016/j.asr.2022.05.062 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Capozziello, Salvatore
AU  - Zakharov, Alexander F.
AU  - Jovanović, Predrag
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9981
AB  - After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first post-Newtonian (pN) approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Extended Gravity theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some Extended Gravity models including power-law f(R), general Yukawa-like corrections, scalar–tensor gravity, and non-local gravity theories formulated in both metric and Palatini formalism. In this consideration, we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these Extended Gravity models for which the orbital precession is like in GR. Then we compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, scalar–tensor gravity and non-local gravity theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center.
T2  - Universe
T1  - Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star
VL  - 7
IS  - 11
SP  - 407
DO  - 10.3390/universe7110407
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Capozziello, Salvatore and Zakharov, Alexander F. and Jovanović, Predrag",
year = "2021",
abstract = "After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first post-Newtonian (pN) approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Extended Gravity theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some Extended Gravity models including power-law f(R), general Yukawa-like corrections, scalar–tensor gravity, and non-local gravity theories formulated in both metric and Palatini formalism. In this consideration, we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these Extended Gravity models for which the orbital precession is like in GR. Then we compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, scalar–tensor gravity and non-local gravity theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center.",
journal = "Universe",
title = "Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star",
volume = "7",
number = "11",
pages = "407",
doi = "10.3390/universe7110407"
}

Borka, D., Borka Jovanović, V., Capozziello, S., Zakharov, A. F.,& Jovanović, P.. (2021). Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star. in Universe, 7(11), 407.
https://doi.org/10.3390/universe7110407

Borka D, Borka Jovanović V, Capozziello S, Zakharov AF, Jovanović P. Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star. in Universe. 2021;7(11):407.
doi:10.3390/universe7110407 .

Borka, Duško, Borka Jovanović, Vesna, Capozziello, Salvatore, Zakharov, Alexander F., Jovanović, Predrag, "Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star" in Universe, 7, no. 11 (2021):407,
https://doi.org/10.3390/universe7110407 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
AU  - Capozziello, Salvatore
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9802
AB  - We use the Fundamental Plane of Elliptical Galaxies to constrain the so-called Hybrid Gravity, a modified theory of gravity where General Relativity is improved by further degrees of freedom of metric-affine Palatini formalism of f(R) gravity. Because the Fundamental Plane is connected to the global properties of elliptical galaxies, it is possible to obtain observational constraints on the parameters of Hybrid Gravity in the weak field limit. We analyze also the velocity distribution of elliptical galaxies comparing our theoretical results in the case of Hybrid Gravity with astronomical data for elliptical galaxies. In this way, we are able to constrain the Hybrid Gravity parameters mϕ and ϕ. We show that the Fundamental Plane, i.e., vc/ σ relations, can be used as a standard tool to probe different theories of gravity in the weak field limit. We conclude that Hybrid Gravity is able to explain elliptical galaxies with different stellar kinematics without the dark matter hypothesis. © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T1  - Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies
VL  - 75
IS  - 5
DO  - 10.1140/epjd/s10053-021-00163-y
ER  - 

@article{
author = "Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag and Capozziello, Salvatore",
year = "2021",
abstract = "We use the Fundamental Plane of Elliptical Galaxies to constrain the so-called Hybrid Gravity, a modified theory of gravity where General Relativity is improved by further degrees of freedom of metric-affine Palatini formalism of f(R) gravity. Because the Fundamental Plane is connected to the global properties of elliptical galaxies, it is possible to obtain observational constraints on the parameters of Hybrid Gravity in the weak field limit. We analyze also the velocity distribution of elliptical galaxies comparing our theoretical results in the case of Hybrid Gravity with astronomical data for elliptical galaxies. In this way, we are able to constrain the Hybrid Gravity parameters mϕ and ϕ. We show that the Fundamental Plane, i.e., vc/ σ relations, can be used as a standard tool to probe different theories of gravity in the weak field limit. We conclude that Hybrid Gravity is able to explain elliptical galaxies with different stellar kinematics without the dark matter hypothesis. © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.",
journal = "European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics",
title = "Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies",
volume = "75",
number = "5",
doi = "10.1140/epjd/s10053-021-00163-y"
}

Borka Jovanović, V., Borka, D., Jovanović, P.,& Capozziello, S.. (2021). Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75(5).
https://doi.org/10.1140/epjd/s10053-021-00163-y

Borka Jovanović V, Borka D, Jovanović P, Capozziello S. Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics. 2021;75(5).
doi:10.1140/epjd/s10053-021-00163-y .

Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, Capozziello, Salvatore, "Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies" in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75, no. 5 (2021),
https://doi.org/10.1140/epjd/s10053-021-00163-y . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Zakharov, Alexander F.
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9803
AB  - In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter, and we require that the value of orbital precession is the same like in general relativity (GR). From that request we determine gravity parameter λ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter λ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter λ of the Yukawa gravity model, and to constrain the graviton mass. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T1  - Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity
VL  - 75
IS  - 5
DO  - 10.1140/epjd/s10053-021-00154-z
ER  - 

@article{
author = "Jovanović, Predrag and Borka, Duško and Borka Jovanović, Vesna and Zakharov, Alexander F.",
year = "2021",
abstract = "In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter, and we require that the value of orbital precession is the same like in general relativity (GR). From that request we determine gravity parameter λ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter λ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter λ of the Yukawa gravity model, and to constrain the graviton mass. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.",
journal = "European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics",
title = "Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity",
volume = "75",
number = "5",
doi = "10.1140/epjd/s10053-021-00154-z"
}

Jovanović, P., Borka, D., Borka Jovanović, V.,& Zakharov, A. F.. (2021). Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75(5).
https://doi.org/10.1140/epjd/s10053-021-00154-z

Jovanović P, Borka D, Borka Jovanović V, Zakharov AF. Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics. 2021;75(5).
doi:10.1140/epjd/s10053-021-00154-z .

Jovanović, Predrag, Borka, Duško, Borka Jovanović, Vesna, Zakharov, Alexander F., "Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity" in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75, no. 5 (2021),
https://doi.org/10.1140/epjd/s10053-021-00154-z . .