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Zhaoyi Xu

Publications and source records attributed to Zhaoyi Xu.

75 records · Page 5Linked to original sources

Kerr-Newman-AdS Black Hole In Quintessential Dark Energy

Quintessential dark energy with pressure $p$ and density $ρ$ is related by equation of state $p=ωρ$ with the state parameter $-1<ω<-1/3$. The cosmological dark energy influence on black hole spacetime are interesting and important. In this paper, we study the Kerr-Newman-AdS solutions of the Einstein-Maxwell equation in quintessence field around a black hole by Newman-Janis algorithm and complex computations. From the horizon structure equation, we obtain the expression between quintessence parameter $α$ and cosmological constant $Λ$ if the black hole exists two cosmological horizon $r_{q}$ and $r_{c}$ when $ω=-2/3$, the result is different from rotational black hole in quintessence matter situation. Through analysis we find that the black hole charge cannot change the value of $α$. But the black hole spin and cosmological constant are opposite. The black hole spin and cosmological constant make the maximum value of $α$ to become small. The existence of four horizon leads seven types of extremal black holes to constraint the parameter $α$. With the state parameter $ω$ ranging from $-1$ to $-1/3$, the maximum value of $α$ changes from $Λ$ to $1$. When $ω\rightarrow -1$, the quintessential dark energy likes cosmological constant. The singularity of the black holes is the same with that of Kerr black hole. We also discuss the rotation velocity of the black holes on the equatorial plane for $ω=-2/3,-1/2$ and $-1/3$. For small value of $α$, the rotation velocity on the equatorial plane is asymptotically flat and it can explain the rotation curves in spiral galaxies.

gr-qc↗

A mathematical form of force-free magnetosphere equation around Kerr black holes and its application to Meissner effect

Based on the Lagrangian of the steady axisymmetric force-free magnetosphere (FFM) equation around Kerr black holes(KBHs), we find that the FFM equation can be rewritten in a new form as $f_{,rr} / (1-μ^{2}) + f_{,μμ} / Δ+ K(f(r,μ),r,μ) = 0$, where $μ= -\cosθ$. By coordinate transformation, the form of the above equation can be given by $s_{,yy} + s_{,zz} + D(s(y,z),y,z) = 0$. Based on the form, we prove finally that the Meissner effect is not possessed by a KBH-FFM with the condition where $dω/d A_ϕ \leqslant 0$ and $H_ϕ(dH_ϕ/dA_ϕ) \geqslant 0$, here $A_ϕ$ is the $ϕ$ component of the vector potential $\vec{A}$, $ω$ is the angular velocity of magnetic fields and ${H_ϕ}$ corresponds to twice the poloidal electric current.

gr-qc↗

Force-free magnetosphere on near-horizon geometry of near-extreme Kerr black holes

We study force-free magnetospheres in the Blandford-Znajek process from rapidly rotating black holes by adopting the near-horizon geometry of near-extreme Kerr black holes (near-NHEK). It is shown that the Znajek regularity condition on the horizon can be directly derived from the resulting stream equation. In terms of the condition, we split the full stream equation into two separate equations. Approximate solutions around the rotation axis are derived. They are found to be consistent with previous solutions obtained in the asymptotic region. The solutions indicate energy and angular-momentum extraction from the hole.

gr-qc↗