Wormholes Supported by a Combination of Normal and Quintessential Matter in Einstein and Einstein-Maxwell Gravity

It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.

A new rotating black hole in quintessential dark energy and its thermodynamics

The spacetime metric for a rotating black hole in a quintessential field can take various forms owing to the ambiguity of the state equation for quintessential dark energy in rotating spacetime. Herein, to provide a more physical solution, the metric is determined by imposing the laws of thermodynamics of a black hole, which is typically valid in most systems. The new metric ensures the validity of the first and second laws of thermodynamics and can degenerate to the known non-rotating metric in the quintessential field. Moreover, we set an upper limit for the black hole rotation parameter, a, in our metric according to the weak energy condition(WEC).

Thermodynamics of black holes in the quintessential phase space

Considering that the negative pressure of the accelerated expansion of the universe results from the cosmological constant or the dark energy quintessence,we use the dark energy quintessence to construct the"quintessential"phase space.In contrast to the previous discussion in which the cosmological constant is considered as the black hole(BH)phase transition pressure,in this analysis,we believe that the pressure results from quintessence.The characteristics of critical behavior,Gibbs free energy,and temperature behavior in quintessential phase space are investigated.We observe that the phase transition belongs to van der Waals phase transition within-1<ωq<-2/3.Ifωqis within(–2/3,–1/3),the phase transition loses the large BH phase transition characteristics,which is caused by the later stage of the phase transition being completely dominated by quintessence dark energy with negative pressure.These results suggest that the quintessential phase space can be constructed with the pressure from the thermal quintessence,and it can be used as a new probe to explore the thermodynamics of BHs.

Test particles and quasiperiodic oscillations around Kiselev black hole with cloud of strings

In the present study,we investigate the dynamics of test particles around a Schwarzschild black hole surrounded by quintessence and immersed in a scalar string cloud field.We start our study by defining the possible values of the quintessence and cloud of string parameters corresponding to the existence of the black hole horizon for fixed values of the parameters of the equation of state for dark energy.We also study the effects of the effective potential on the circular motion,energy,and angular momentum of the test particles together with the innermost stable circular orbits(ISCOs).We investigate the fundamental frequencies in the particle oscillations along stable circular orbits.We relate the stability of the orbits to the Lyapunov exponent,and the chaotic behavior is studied graphically.Finally,we apply the fundamental frequencies to describe quasiperiodic oscillations(QPOs)and find that,in the presence of both fields,low-frequency twin-peak QPOs are not observed.In addition,we obtain the constraint values for the string cloud parameter and mass of the black hole candidates located in the center of the microquasars GRO J1655-40 and GRS 1915+105 as well as the Milky Way galaxy.

Erratum:Corrigendum to"Effect of dark energy models on the energy content of charged and rotating black holes"[Chinese Phys.C,46(2022)015101]

In Liaqat and Hussain(2022)it was proved that the effect of dark energy with w_(n)=1/3 causes a reduction in the energy content of the quintessential charged-Kerr spacetime.This result needs correction as it is observed that the contribution of dark energy first decreases the total energy of the underlying spacetime for smaller values of radial coordinate r and then increases the energy for comparatively larger values of r.