Destroying a near-extremal Kerr-Newman black hole

Saa, Alberto; Santarelli, Raphael

doi:10.1103/physrevd.84.027501

Cited by 129 publications

(134 citation statements)

References 36 publications

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“…Similar potential violations of (1) have been found for Reissner-Nordström black holes absorbing angular momentum [5], Kerr black holes absorbing charge or angular momentum [6][7][8], and for generic Kerr-Newman black holes [9,10]. However, just as in Hubeny's argument, in order to determine whether these potential violations actually occur, one needs to calculate all contributions to energy that are quadratic order in the relevant parameters of the particle.…”

Section: Introductionmentioning

confidence: 54%

“…9 If we wish to take Σ 1 to extend infinitely far from the black hole, we would have to take it to null infinity rather than spatial infinity. 10 Note that since mass and angular momentum cannot be radiated away at linear order, we did not need to be careful in our specification of Σ 1 in our first order analysis in order for δM and δJ to represent the perturbed mass and angular momentum of the final black hole.…”

Section: Gedanken Experiments To Destroy a Slightly Non-extremal mentioning

confidence: 99%

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Gedanken experiments to destroy a black hole. II. Kerr-Newman black holes cannot be overcharged or overspun

2017

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We consider gedanken experiments to destroy an extremal or nearly extremal Kerr-Newman black hole by causing it to absorb matter with sufficient charge and/or angular momentum as compared with energy that it cannot remain a black hole. It was previously shown by one of us that such gedanken experiments cannot succeed for test particle matter entering an extremal Kerr-Newman black hole. We generalize this result here to arbitrary matter entering an extremal Kerr-Newman black hole, provided only that the non-electromagnetic contribution to the stressenergy tensor of the matter satisfies the null energy condition. We then analyze the gedanken experiments proposed by Hubeny and others to over-charge and/or over-spin an initially slightly non-extremal Kerr-Newman black hole. Analysis of such gedanken experiments requires that we calculate all effects on the final mass of the black hole that are second-order in the charge and angular momentum carried into the black hole, including all self-force effects. We obtain a general formula for the full second order correction to mass, δ 2 M , which allows us to prove that no gedanken experiments of the generalized Hubeny type can ever succeed in over-charging and/or over-spinning a Kerr-Newman black hole, provided only that the non-electromagnetic stress-energy tensor satisfies the null energy condition. Our analysis is based upon Lagrangian methods, and our formula for the second-order correction to mass is obtained by generalizing the canonical energy analysis of Hollands and Wald to the Einstein-Maxwell case. Remarkably, we obtain our formula for δ 2 M without having to explicitly compute self-force or finite size effects. Indeed, in an appendix, we show explicitly that our formula incorporates both the self-force and finite size effects for the special case of a charged body slowly lowered into an uncharged black hole.2

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Section: Introductionmentioning

confidence: 54%

Section: Gedanken Experiments To Destroy a Slightly Non-extremal mentioning

confidence: 99%

Gedanken experiments to destroy a black hole. II. Kerr-Newman black holes cannot be overcharged or overspun

2017

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“…The possibility of turning a black hole into a naked singularity by accretion of different types of particles was analysed in several theoretical researches, and a variety of conclusions have been proposed: from works finding that an extreme black hole cannot accrete particles that would make its horizon disappear to works that contradict this conclusion by analysing accretion of test particles by nearly extreme black holes (see, for example, Wald 1974a;Hubeny 1999;de Felice & Yunqiang 2001;Jacobson & Sotiriou 2009;Saa & Santarelli 2011, for studies related to Kerr and Reissner-Nordström solutions).…”

Section: Introductionmentioning

confidence: 99%

Magnetised accretion discs in Kerr spacetimes

Ranea‐Sandoval

García

2015

A&A

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Context. Observational data from X-ray binary systems provide strong evidence of astronomical objects that are too massive and compact to be explained as neutron or hybrid stars. When these systems are in the thermal (high/soft) state, they emit mainly in the 0.1−5 keV energy range. This emission can be explained by thin accretion discs that formed around compact objects like black holes. The profile of the fluorescent iron line is useful to obtain insight into the nature of the compact object. General relativity does not ensure that a black hole must form after the complete gravitational collapse of very massive stars, and other theoretical models such as naked singularities cannot be discarded. The cosmic censorship conjecture was proposed by Penrose to avoid these possibilities and is yet to be proven. Aims. We study the effect caused by external magnetic fields on the observed thermal spectra and iron line profiles of thin accretion discs formed around Kerr black holes and naked singularities. We aim to provide a tool that can be used to estimate the presence of magnetic fields in the neighbourhood of a compact object and to probe the cosmic censorship conjecture in these particular astrophysical environments. Methods. We developed a numerical scheme able to calculate thermal spectra of magnetised Page-Thorne accretion discs formed around rotating black holes and naked singularities as seen by an arbitrary distant observer. We incorporated two different magnetic field configurations: uniform and dipolar, using a perturbative scheme in the coupling constant between matter and magnetic field strength. Under the same assumptions, we obtained observed synthetic line profiles of the 6.4 keV fluorescent iron line. Results. We show that an external magnetic field produces potentially observable modifications on the thermal energy spectrum and the fluorescent iron line profile. Thermal energy spectra of naked singularities are harder and brighter than those from black holes, and in addition, peak and cut-off energies are affected by the external magnetic field. Moreover, iron line profiles of slowly rotating black holes suffer more changes by a uniform magnetic field, while nearly extremal black holes and naked singularities are more altered in the dipolar case. Based on our calculations, we discard the possibility of modelling the archetypal black-hole candidate in Cygnus X-1 as a naked singularity. Conclusions. Comparison of our models with observational data can be used to probe the cosmic censorship conjecture and to estimate the existence and global geometry of magnetic fields around compact objects by fitting the thermal energy spectra and iron line profiles of X-ray binaries.

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“…The range of parameter b is given in [3,4]. As shown in [2] the allowed range for the uncharged particle to enter the black hole is given by [3, √ 12].…”

Section: Particle Motion Around Near-extremal Kerr Black Holementioning

confidence: 99%

“…It was also shown that it would be possible to destroy near-extremal Reissner-Nordström black holes with charged test particle [3]. The process of destroying rotating black hole with the charged test particle was investigated in [4]. In all these calculations it was assumed that the test particle follows a geodesic motion and effects of the conservative and dissipative backreaction were ignored.…”

Section: Introductionmentioning

confidence: 99%

Destroying a near-extremal Kerr black hole with a charged particle: Can a test magnetic field serve as a cosmic censor?

et al. 2015

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We investigate effect of a test magnetic field on the process of destroying near-extremal Kerr black hole with a charged test particle. It has been shown that it would be possible to throw a charged test particle into the near extremal rotating black hole and make it go past the extremality i.e. turn Kerr black hole into the Kerr-Newmann naked singularity. Typically in an astrophysical scenario black holes are believed to be surrounded by a magnetic field. Magnetic field although small, affects motion of charged particles drastically due to the large Lorentz force, as the electromagnetic force is much stronger that the gravity. Thus a test magnetic field can affect the process of destroying black holes and restore the cosmic censorship in the astrophysical context. We show that a test magnetic field would act as a cosmic censor beyond a certain threshold value. We try to gauge the magnitude of the magnetic field by comparing its energy density with that of the change in the curvature induced by the test particle. We find that the magnetic field required in only as strong as or slightly stronger as compared to the value for which its effect of the background geometry is comparable to the tiny backreaction as that of the test particle. In such a case however one has to take take into account effect of the magnetic field on the background geometry, which is difficult to implement in the absence of any exact near-extremal rotating magnetized black hole solutions. We argue that magnetic field would still act as a cosmic censor.

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Destroying a near-extremal Kerr-Newman black hole

Cited by 129 publications

References 36 publications

Gedanken experiments to destroy a black hole. II. Kerr-Newman black holes cannot be overcharged or overspun

Gedanken experiments to destroy a black hole. II. Kerr-Newman black holes cannot be overcharged or overspun

Magnetised accretion discs in Kerr spacetimes

Destroying a near-extremal Kerr black hole with a charged particle: Can a test magnetic field serve as a cosmic censor?

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