Quasiperiodic oscillations around rotating traversable wormholes

AbstractA strong quasi-periodic modulation has recently been revealed in the X-ray flux of the X-ray source XMMUJ134736.6+173403. The two observed twin-peak quasiperiodic oscillations (QPOs) exhibit a 3:1 frequency ratio and strongly support the evidence for the presence of an active galactic nucleus black hole (AGN BH). It has been suggested that detections of twin-peak QPOs with commensurable frequency ratios and scaling of their periods with BH mass could provide the basis for a method intended to determine the mass of BH sources, such as AGNs. Assuming the orbital origin of QPOs, we calculate the upper and lower limit on the AGN BH mass M, reaching M ≍ 107–109M⊙. Compared to mass estimates of other sources, XMMUJ134736.6+173403 appears to be the most massive source with commensurable QPO frequencies, and its mass represents the current observational upper limit on the AGN BH mass obtained from the QPO observations.

Download Full-text

Gravitational lensing effect in traversable wormholes

Annals of Physics ◽

10.1016/j.aop.2021.168460 ◽

2021 ◽

pp. 168460

Author(s):

Nisha Godani ◽

Gauranga C. Samanta

Keyword(s):

Gravitational Lensing ◽

Traversable Wormholes ◽

Lensing Effect

Download Full-text

Traversable wormholes in Einsteinian cubic gravity

Modern Physics Letters A ◽

10.1142/s0217732320500170 ◽

2019 ◽

Vol 35 (06) ◽

pp. 2050017 ◽

Cited By ~ 7

Author(s):

Mohammad Reza Mehdizadeh ◽

Amir Hadi Ziaie

Keyword(s):

Equation Of State ◽

Gravitational Lensing ◽

Energy Condition ◽

Higher Order ◽

Energy Conditions ◽

Geodesic Motion ◽

De Sitter ◽

Asymptotically Flat ◽

Traversable Wormholes ◽

Standard Energy

In this work, we investigate wormhole configurations described by a constant redshift function in Einstein-Cubic gravity ( ECG ). We derive analytical wormhole geometries by assuming a particular equation of state ( EoS ) and investigate the possibility that these solutions satisfy the standard energy conditions. We introduce exact asymptotically flat and anti-de Sitter (AdS) spacetimes that admit traversable wormholes. These solutions are obtained by imposing suitable values for the parameters of the theory so that the resulted geometries satisfy the weak energy condition ( WEC ) in the vicinity of the throat, due to the presence of higher-order curvature terms. Moreover, we find that AdS solutions satisfy the WEC throughout the spacetime. A description of the geodesic motion of time-like and null particles is presented for the obtained wormhole solutions. Also, using gravitational lensing effects, observational features of the wormhole structure are discussed.

Download Full-text

Traversable wormholes with exponential shape function in modified gravity and general relativity: A comparative study

International Journal of Modern Physics D ◽

10.1142/s0218271820500686 ◽

2020 ◽

Vol 29 (09) ◽

pp. 2050068 ◽

Cited By ~ 3

Author(s):

Gauranga C. Samanta ◽

Nisha Godani ◽

Kazuharu Bamba

Keyword(s):

General Relativity ◽

Equation Of State ◽

Comparative Study ◽

Modified Gravity ◽

Shape Function ◽

Anisotropy Parameter ◽

Energy Conditions ◽

Traversable Wormholes

We have proposed a novel shape function on which the metric that models traversable wormholes is dependent. Using this shape function, the energy conditions, equation-of-state and anisotropy parameter are analyzed in [Formula: see text] gravity, [Formula: see text] gravity and general relativity. Furthermore, the consequences obtained with respect to these theories are compared. In addition, the existence of wormhole geometries is investigated.

Download Full-text

TRAVERSABLE WORMHOLES IN A STRING CLOUD

International Journal of Modern Physics D ◽

10.1142/s0218271808012759 ◽

2008 ◽

Vol 17 (08) ◽

pp. 1179-1196 ◽

Cited By ~ 27

Author(s):

MARTÍN G. RICHARTE ◽

CLAUDIO SIMEONE

Keyword(s):

Thin Shell ◽

Dimensional Space ◽

Space Time ◽

Exotic Matter ◽

Spherically Symmetric ◽

Related Model ◽

Traversable Wormholes ◽

Dimensional Space Time ◽

Thin Shell Wormholes ◽

The Stability

We study spherically symmetric thin shell wormholes in a string cloud background in (3 + 1)-dimensional space–time. The amount of exotic matter required for the construction, the traversability and the stability of such wormholes under radial perturbations are analyzed as functions of the parameters of the model. In addition, in the appendices a nonperturbative approach to the dynamics and a possible extension of the analysis to a related model are briefly discussed.

Download Full-text

NEGATIVE ENERGY DENSITY IN SPINNING MATTER SOURCES IN WORMHOLE SPACE–TIMES WITH TORSION

Modern Physics Letters A ◽

10.1142/s0217732398003260 ◽

1998 ◽

Vol 13 (38) ◽

pp. 3069-3072

Author(s):

L. C. GARCIA DE ANDRADE

Keyword(s):

Energy Density ◽

Spin Density ◽

Gravitational Collapse ◽

Negative Pressure ◽

Negative Energy ◽

Space Time ◽

Negative Energy Density ◽

Traversable Wormholes ◽

Radial Tension

Negative energy densities in spinning matter sources of non-Riemannian ultrastatic traversable wormholes require the spin energy density to be higher than the negative pressure or the radial tension. Since the radial tension necessary to support wormholes is higher than the spin density in practice, it seems very unlikely that wormholes supported by torsion may exist in nature. This result corroborates earlier results by Soleng against the construction of the closed time-like curves (CTC) in space–time geometries with spin and torsion. It also agrees with earlier results by Kerlick according to which Einstein–Cartan (EC) gravity torsion sometimes enhance the gravitational collapse instead of avoiding it.

Download Full-text