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The Zipoy-Voorhees solution is known as the γ-metric and/or q-metric being static and axisymmetric vacuum solution of Einstein field equations which becomes strong curvature naked singularity. The metric is characterized by two parameters, namely, the mass M and the dimensionless deformation parameter γ. It is shown that the velocity of test partic...
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Context 1
... at negative ISCO, it even might be greater than the speed of light for the specific values of the γ parameter. Figure 1 shows the dependence of the orbital velocity of the particle, v ± , at the ISCO positions from the γ parameter. One can see that the maximum value for the velocity at the positive ISCO is v + ≤ c/ √ 2 0.7c for γ = 1/ √ 5, while for the large value of the γ parameter, it will be v + = c √ 5 − 2 0.486c. ...
Context 2
... can see that the maximum value for the velocity at the positive ISCO is v + ≤ c/ √ 2 0.7c for γ = 1/ √ 5, while for the large value of the γ parameter, it will be v + = c √ 5 − 2 0.486c. Interestingly, as we see from Figure 1, the velocity of particle at the negative ISCO may reach the speed of light, i.e., v − = c at γ = 1/2, while it is greater than the speed of light for γ > 1/2 that leads to causality problem. Here, one might conclude that there is a tool/mechanism for the possible generation of tachyon which is a purely hypothetical particle with the superluminal velocity being greater than the speed of light. ...
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A bstract
In this work, we consider a very simple gravitational theory that contains a scalar field with its kinetic and potential terms minimally coupled to gravity, while the scalar field is assumed to have a coulombic form. In the context of this theory, we study an analytic, asymptotically flat, and regular (ultra-compact) black-hole solutions...
Citations
... It is also interesting to consider the orbital velocity of the test particles as measured by a local frame. In Ref. [59], it was shown that the orbital velocity of test particles in the γ metric is given by ...
We study matter accretion in a static, axially symmetric and vacuum geometry describing the exterior gravitational field of a black hole mimicker called the γ metric. We evaluate the thermal and optical properties of thin accretion disks, including the emission rate, luminosity and shadow, in the gamma spacetime. Also, we explore the radial accretion of polytropic matter fields onto the central source and evaluate the thermal and optical properties of the infalling gas, such as temperature and luminosity. The results are discussed in the context of evaluating the possibility that the true nature of astrophysical black hole candidates may not be a black hole but some exotic compact object possessing a non-vanishing mass quadrupole moment.
... In other words, the γ-metric is an appealing candidate to describe spacetimes close to Schwarzschild, by means of exact analytical solutions to Einstein vacuum equations. This of course is of utmost relevance and explains why it has been so extensively studied in the past (see [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] and the references therein). ...
Citation: Herrera, L.; Di Prisco, A.; Ospino, J.; Carot, J. Quasi-Hyperbolically Symmetric γ-Metric. Entropy 2023, 25, 1338. https:// Abstract: We carry out a systematic study on the motion of test particles in the region inner to the naked singularity of a quasi-hyperbolically symmetric γ-metric. The geodesic equations are written and analyzed in detail. The obtained results are contrasted with the corresponding results obtained for the axially symmetric γ-metric and the hyperbolically symmetric black hole. As in this latter case, it is found that test particles experience a repulsive force within the horizon (naked singularity), which prevents them from reaching the center. However, in the present case, this behavior is affected by the parameter γ which measures the departure from the hyperbolical symmetry. These results are obtained for radially moving particles as well as for particles moving in the θ − r subspace. The possible relevance of these results in the explanation of extragalactic jets is revealed.
... In other words, the γ-metric is an appealing candidate to describe space-times close to Schwarzschild, by means of exact analytical solutions to Einstein vacuum equations. This of course is of utmost relevance and explains why it has been so extensively studied in the past (see [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] and references therein). ...
We carry out a systematic study on the motion of test particles in the region inner to the naked singularity of a quasi–hyperbolically symmetric γ-metric. The geodesic equations are written and analyzed in detail. The obtained results are contrasted with the corresponding results obtained for the axially symmetric γ-metric, and the hyperbolically symmetric black hole. As in this latter case, it is found that test particles experience a repulsive force within the horizon (naked singularity), which prevents them to reach the center. However in the present case this behavior is affected by the parameter γ which measures the departure from the hyperbolical symmetry. These results are obtained for radially moving particles as well as for particles moving in the θ−r subspace. Possible relevance of these results in the explanation of extragalactic jets, is brought out. .
... Professors teaching this material are not happy with its consequences, even in modern times, as in [25] where it was declared "In concluding, it is important to emphasize that the interior structure of realistic black holes has not been satisfactorily determined and is still open to considerable debate". Another metric [26] is introduced with ma-International Journal of Astronomy and Astrophysics thematical consequences related to the existence of the superluminal particles called tachyons. ...
Obviously, from the geometrical point of view, it is impossible to distinguish the electrically and magnetically charged Reissner–Nordström black holes. One way of describing the differences between these solutions is to study the dynamical motion of charged test particles in the vicinity of the charged black hole and explore the effects of the charge coupling parameters (σe,σm) on the instability of the circular orbits. On the other hand, it is also possible to investigate the fundamental frequencies, such as Keplerian, Larmor, and epicyclic frequencies of charged particles orbiting around a charged black hole. Lastly, we investigate the synchrotron radiation by charged particles accelerated by charged black hole and estimate the intensity of relativistic radiating charged particles. Finally, we comment on the possible utilization of our findings for the relativistic jets and magneto-hydrodynamical outflows.
