scholarly journals Can accretion properties distinguish between a naked singularity, wormhole and black hole?

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
R. Kh. Karimov ◽  
R. N. Izmailov ◽  
A. A. Potapov ◽  
K. K. Nandi

AbstractWe first advance a mathematical novelty that the three geometrically and topologically distinct objects mentioned in the title can be exactly obtained from the Jordan frame vacuum Brans I solution by a combination of coordinate transformations, trigonometric identities and complex Wick rotation. Next, we study their respective accretion properties using the Page–Thorne model which studies accretion properties exclusively for $$r\ge r_{\text {ms}}$$ r ≥ r ms (the minimally stable radius of particle orbits), while the radii of singularity/throat/horizon $$r<r_{\text {ms}}$$ r < r ms . Also, its Page–Thorne efficiency $$\epsilon $$ ϵ is found to increase with decreasing $$r_{\text {ms}}$$ r ms and also yields $$\epsilon =0.0572$$ ϵ = 0.0572 for Schwarzschild black hole (SBH). But in the singular limit $$r\rightarrow r_{s}$$ r → r s (radius of singularity), we have $$\epsilon \rightarrow 1$$ ϵ → 1 giving rise to $$100 \%$$ 100 % efficiency in agreement with the efficiency of the naked singularity constructed in [10]. We show that the differential accretion luminosity $$\frac{d{\mathcal {L}}_{\infty }}{d\ln {r}}$$ d L ∞ d ln r of Buchdahl naked singularity (BNS) is always substantially larger than that of SBH, while Eddington luminosity at infinity $$L_{\text {Edd}}^{\infty }$$ L Edd ∞ for BNS could be arbitrarily large at $$r\rightarrow r_{s}$$ r → r s due to the scalar field $$\phi $$ ϕ that is defined in $$(r_{s}, \infty )$$ ( r s , ∞ ) . It is concluded that BNS accretion profiles can still be higher than those of regular objects in the universe.

2019 ◽  
Vol 27 (3) ◽  
pp. 231-241
Author(s):  
Ivan M. Potashov ◽  
Julia V. Tchemarina ◽  
Alexander N. Tsirulev

We study the geodesics motion of neutral test particles in the static spherically symmetric spacetimes of black holes and naked singularities supported by a selfgravitating real scalar field. The scalar field is supposed to model dark matter surrounding some strongly gravitating object such as the centre of our Galaxy. The behaviour of timelike and null geodesics very close to the centre of such a configuration crucially depends on the type of spacetime. It turns out that a scalar field black hole, analogously to a Schwarzschild black hole, has the innermost stable circular orbit and the (unstable) photon sphere, but their radii are always less than the corresponding ones for the Schwarzschild black hole of the same mass; moreover, these radii can be arbitrarily small. In contrast, a scalar field naked singularity has neither the innermost stable circular orbit nor the photon sphere. Instead, such a configuration has a spherical shell of test particles surrounding its origin and remaining in quasistatic equilibrium all the time. We also show that the characteristic properties of null geodesics near the centres of a scalar field naked singularity and a scalar field black hole of the same mass are qualitatively different.


2016 ◽  
Vol 31 (26) ◽  
pp. 1650151 ◽  
Author(s):  
Katsutaro Shimizu

We propose a gravitational energy–momentum (GEMT) tensor of the general relativity obtained using Noether’s theorem. It transforms as a tensor under general coordinate transformations. One of the two indices of the GEMT labels a local Lorentz frame that satisfies the energy–momentum conservation law. The energies for a gravitational wave, a Schwarzschild black hole and a Friedmann–Lemaitre–Robertson–Walker (FLRW) universe are calculated as examples. The gravitational energy of the Schwarzschild black hole exists only outside the horizon, its value being the negative of the black hole mass.


1997 ◽  
Vol 06 (01) ◽  
pp. 91-105 ◽  
Author(s):  
M. D. Pollock

The Wheeler–DeWitt equation for the wave function ψ is obtained from the two-dimensional world-sheet action for the bosonic string and the superstring, including higher-derivative terms, as the Schrödinger equation i ∂ ψ/ ∂τ = V(τ)ψ. The potential is given by the rate at which the world-sheet area is swept out, V(τ) = dA(τ)/dτ, and is positive semi-definite, allowing the existence of a ground state, corresponding to the absence of the string, with a non-vanishing probability density ψ ψ*. Integration of this equation yields the solution [Formula: see text], where [Formula: see text] is the action, minus the higher-derivative terms [Formula: see text] (and terms involving ∊ab in the case of the superstring), which, however, are constrained to vanish semi-classically, being constructed from the square of the equation of motion for the bosonic coordinates XA derived from [Formula: see text] alone. This path-integral expression for ψ is consistent with the operator replacements for the canonical momenta used in its derivation, and forms the basis of the approach due to Polyakov of summing over random surfaces. Comparison is made with the Schrödinger equations derived previously from the reduced, four-dimensional effective action for the heterotic superstring, and for the Schwarzschild black hole (by Tomimatsu), where the potential is also positive semi-definite, being (twice) the total mass of the Universe and the mass of the black hole, respectively, showing the unity of the method.


Author(s):  
K.A.I.L. Wijewardena Gamalath ◽  
N.S. Rajapakse

A simple model was setup to find the mass variation over time for a Schwarzschild black hole. The temperature and entropy of a black hole was obtained from the numerically solved mass variation and the time variations of the black hole thermodynamic parameters were simulated. The mass of a given black hole reduces rapidly. The time taken for a black hole to vanish increases in an increasing rate with the given initial mass of the black hole. The temperature of a black hole drastically increases at the final stage of the black hole evaporation. The colour attributed to that temperature was found to be in the visible region for a significant amount of time. The black hole entropy also drastically reduces with its mass and through Hawking radiation it is added to the rest of the universe.


2019 ◽  
Vol 27 (3) ◽  
pp. 231-241
Author(s):  
Ivan M. Potashov ◽  
Julia V. Tchemarina ◽  
Alexander N. Tsirulev

We study the geodesics motion of neutral test particles in the static spherically symmetric spacetimes of black holes and naked singularities supported by a selfgravitating real scalar field. The scalar field is supposed to model dark matter surrounding some strongly gravitating object such as the centre of our Galaxy. The behaviour of timelike and null geodesics very close to the centre of such a configuration crucially depends on the type of spacetime. It turns out that a scalar field black hole, analogously to a Schwarzschild black hole, has the innermost stable circular orbit and the (unstable) photon sphere, but their radii are always less than the corresponding ones for the Schwarzschild black hole of the same mass; moreover, these radii can be arbitrarily small. In contrast, a scalar field naked singularity has neither the innermost stable circular orbit nor the photon sphere. Instead, such a configuration has a spherical shell of test particles surrounding its origin and remaining in quasistatic equilibrium all the time. We also show that the characteristic properties of null geodesics near the centres of a scalar field naked singularity and a scalar field black hole of the same mass are qualitatively different.


Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 177
Author(s):  
Rosaliya M. Yusupova ◽  
Ramis Kh. Karimov ◽  
Ramil N. Izmailov ◽  
Kamal K. Nandi

Study of accretion onto wormholes is rather rare compared to that onto black holes. In this paper, we consider accretion flow of cosmological dark energy modeled by barotropic fluid onto the celebrated Ellis–Bronnikov wormhole (EBWH) built by Einstein minimally coupled scalar field ϕ, violating the null energy condition. The accreting fluid is assumed to be phantom, quintessence, dust and stiff matter. We begin by first pointing out a mathematical novelty showing how the EBWH can lead to the Schwarzschild black hole under a complex Wick rotation. Then, we analyze the profiles of fluid radial velocity, density and the rate of mass variation of the EBWH due to accretion and compare the profiles with those of the Schwarzschild black hole. We also analyze accretion to the massless EBWH that has zero ADM mass but has what we call nonzero Wheelerian mass (“mass without mass”), composed of the non-trivial scalar field, that shows gravitational effects. Our conclusion is that the mass of SBH due to phantom accretion decreases consistently with known results, while, in contrast, the mass of EBWH increases. Exactly an opposite behavior emerges for non-phantom accretion to these two objects. Accretion to massless EBWH (i.e., to nonzero Wheelerian mass) shares the same patterns as those of the massive EBWH; hence there is no way to distinguish massive and massless cases by means of accretion flow. The contrasting mass variations due to phantom accretion could be a reflection of the distinct topology of the central objects.


2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Alina Khaybullina ◽  
Ramil Izmailov ◽  
Kamal K. Nandi ◽  
Carlo Cattani

We will confront some static spherically symmetric vacuum Brans-Dicke solutions in the Jordan and Einstein Frames with the Robertson parameters. While the regular solution in the vacuum Einstein theory is just the Schwarzschild black hole, the same in the Jordan frame Brans-Dicke theory is shown to represent not a black hole but a traversable wormhole. But, in this case, the valid range ofωbecomes too narrow to yield the observed weak field Robertson parameters at the positive mass mouth. The corresponding solution in the Einstein frame also provides a regular wormhole, and it yields the correct parametric values but only up to “one and half order.” We argue that a second-order contribution can in principle distinguish between the signatures of the regular wormhole and the singular Buchdahl solution in the Einstein frame. Thus, at the level of regular solutions, Brans-Dicke theory in each frame predicts effects very different from those of Einstein's theory. To our knowledge, these theoretical distinctions seem not to have received adequate attention so far.


Author(s):  
Ivan M. Potashov ◽  
Julia V. Tchemarina ◽  
Alexander N. Tsirulev

We study the geodesics motion of neutral test particles in the static spherically symmetric spacetimes of black holes and naked singularities supported by a selfgravitating real scalar field. The scalar field is supposed to model dark matter surrounding some strongly gravitating object such as the centre of our Galaxy. The behaviour of timelike and null geodesics very close to the centre of such a configuration crucially depends on the type of spacetime. It turns out that a scalar field black hole, analogously to a Schwarzschild black hole, has the innermost stable circular orbit and the (unstable) photon sphere, but their radii are always less than the corresponding ones for the Schwarzschild black hole of the same mass; moreover, these radii can be arbitrarily small. In contrast, a scalar field naked singularity has neither the innermost stable circular orbit nor the photon sphere. Instead, such a configuration has a spherical shell of test particles surrounding its origin and remaining in quasistatic equilibrium all the time. We also show that the characteristic properties of null geodesics near the centres of a scalar field naked singularity and a scalar field black hole of the same mass are qualitatively different.


2007 ◽  
Vol 16 (06) ◽  
pp. 1087-1108
Author(s):  
MARCO PIZZI

A new exact solution of the coupled Einstein–Maxwell equations is given and studied. It is found using the soliton method, adding one soliton to the Schwarzschild background. The solution is stationary and axial-symmetric, and has five physical parameters. The physical interpretation we give is that it describes a Kerr–Newman (KN) naked singularity linked by a "strut" to a charged black hole. Indeed, on the axis, between the two bodies an unavoidable anomaly region is present (gφφ < 0 and a conic singularity). The solution is stationary also in the case with zero total angular momentum. Finally, we give the force lines of the electrical field in a general case, and in the case in which the KN singularity has a much smaller mass than the nearby black hole; we also considered the behavior at different distances of the charge. In spite of the naive interpretation suggested by the mathematical construction of the solution, what we expected to be a "Schwarzschild" black hole appears to be charged and rotating; we interpret this fact as a parameter-mixing phenomenon.


Sign in / Sign up

Export Citation Format

Share Document