The higher dimensional Myers-Perry black hole with single rotation always obeys the Cosmic Censorship Conjecture

Even though the Myers-Perry five dimensional rotating black hole with two rotations could be overspun by test particle accretion, yet it turns out as we show in this letter that it cannot do so for a single rotation. On the other hand it is known that there exists no extremal limit for a black hole with single rotation in dimensions greater than equal to six. It has been proven that all higher dimensional ($>4$) rotating black holes with only one single rotation can never be overspun under test particle linear accretion and hence would always obey CCC in the weak form.Comment: 5 pages, no figures; Coincides with published versio

Weak cosmic censorship conjecture in the pure Lovelock gravity

It is well known that a rotating black hole in four dimension could be overspun by linear order test particle accretion which however always gets overturned when non-linear perturbations are included. It turns out that in the Einstein gravity, repulsion due to rotation dominates over attraction due to mass in dimensions, $D>5$, and consequently black hole cannot be overspun even for linear order accretion. For the pure Lovelock rotating black hole, this dimensional threshold is $D>4N+1$ where $N$ is degree of single $N$th order term in the Lovelock polynomial in the action. Thus the pure Lovelock rotating black holes always obey the weak cosmic censorship conjecture (WCCC) in all dimensions greater than $4N+1$. Since overall gravity being repulsive beyond this dimensional threshold, how is rotating black hole then formed?Comment: 9 pages, 1 figur

Like Black holes, Buchdahl stars cannot be extremalized

It was shown long back in \cite{Dadhich97} that a non-extremal black hole cannot be converted into an extremal one by test particle adiabatic accretion. The Buchdahl star is the most compact object without horizon and is defined by $\Phi(R) = 4/9$, while black hole by $\Phi(R) = 1/2$. Here $\Phi(R)$ is the gravitational potential experienced by a particle, radially falling for static and axially for the rotating object. In this short note we examine the question of extremalization of the Buchdhal star and show that the same result holds good as for the black hole. That is, a non-extremal Buchdahl star cannot be extremalized by test particle accretion. Further since extremal limit for BS is $>1$, it could facilitate formation of extremal black holes by neutral and spinless accretion. That is perhaps the only way they could be formed.Comment: 6 pages, 3 captioned figures. Accepted for publication in Phys. Lett.

Overcharging process around a magnetized black hole: Can the backreaction effect of magnetic field restore cosmic censorship conjecture?

It is well known that the electrically charged Reissner-Nordstr\"{o}m black hole could be overcharged. Here, we investigate the process of overcharging of a magnetized Reissner-Nordstr\"{o}m black hole that includes effect of the magnetic field generated by own magnetic charge of source on the background geometry. It is found that magnetic field prevents a transition to occur from black hole to naked singularity, thus overcharging cannot be attained which happens due to the fact that the magnetic field reaches its threshold value. It turns out that beyond threshold value the magnetic field can exert large Lorentz force on particles and dominate over the gravitational force, allowing charged particles not to fall into the black hole. One may conclude, there occurs no evidence for violation of cosmic censorship conjecture for a magnetized Reissner-Nordstr\"{o}m black hole beyond threshold value of the magnetic field.Comment: 10 pages, 3 tables, 3 captioned figures. Accepeted for publication in General Relativity and Gravitatio

Testing the weak cosmic censorship conjecture for a Reissner-Nordstr\"{o}m-de Sitter black hole surrounded by perfect fluid dark matter

In this paper, we test the weak cosmic censorship conjecture (WCCC) for the Reissner-Nordstr\"{o}m-de Sitter (RN-dS) black hole surrounded by perfect fluid dark matter. We consider a spherically symmetric perturbation on deriving linear and non-linear order perturbation inequalities by applying new version of gedanken experiments well accepted from the work of Sorce and Wald. Contrary to the well-known result that the Reissner-Nordstr\"{o}m (RN) black hole could be overcharged under linear order particle accretion it is hereby shown that the same black hole in perfect fluid dark matter with cosmological parameter cannot be overcharged. Considering a realistic scenario in which black holes can not be considered to be in vacuum we investigate the contribution of dark matter and cosmological constant in the overcharging process of an electrically charged black hole. We demonstrate that the black hole can be overcharged only when two fields induced by dark matter and cosmological parameter are completely balanced. Further we give a remarkable result that black hole cannot be overcharged beyond a certain threshold limit for which the effect arising from the cosmological constant dominates over the effect by the perfect fluid dark matter. Thus even for linear accretion process, the black hole cannot always be overcharged and hence obeys the WCCC in general. This result would continues be fulfilled for non-linear order accretion.Comment: 11 pages, one figure; Title changed and corrections made. Accepted for publication in Eur. Phys. J.

A Kerr-Newman-MOG black hole's impact on the magnetic reconnection

In this paper, we study the magnetic reconnection process of energy extraction from a rapidly rotating Kerr-Newman-MOG black hole by investigating the combined effect of black hole charge and the MOG parameter. We explore the energy efficiency of energy extraction and power. Based on an attractive gravitational charge of the MOG parameter $\alpha$ that physically manifests to strengthen black hole gravity we show that the combined effect of the MOG parameter and black hole charge can play an increasingly important role and accordingly lead to high energy efficiency and power for the energy extraction via the magnetic reconnection. Further, we study to estimate the rate of energy extraction under the fast magnetic reconnection by comparing the power of the magnetic reconnection and Blandford-Znajek (BZ) mechanisms. We show that the rate of energy extraction increases as a consequence of the combined effect of black hole charge and MOG parameter. It suggests that magnetic reconnection is significantly more efficient than BZ. In fact, the magnetic reconnection is fueled by magnetic field energy due to the twisting of magnetic field lines around the black hole for the plasma acceleration, and thus MOG parameter gives rise to even more fast spin that can strongly change the magnetic field reconfiguration due to the frame dragging effect. This is how energy extraction is strongly enhanced through the magnetic reconnection, thus making the energy extraction surprisingly more efficient for the Kerr-Newman-MOG black hole than Kerr black hole under the combined effect of black hole charge and MOG parameter.Comment: 15 pages, one table, 7 captioned figure