Force-free magnetosphere attractors for near-horizon extreme and near-extreme limits of Kerr black hole

Camilloni, Filippo; Grignani, G.; Harmark, Troels; Oliveri, Roberto; Orselli, Marta

doi:10.1088/1361-6382/abdf70

Cited by 8 publications

(12 citation statements)

References 30 publications

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“…However, a magnetically-dominated analytic solution to FFE around extreme Kerr background is still missing so far. A first attempt in this direction has been already taken by identifying the attractor solutions to FFE in the near-horizon region of extreme Kerr [60], and near-extreme Kerr spacetime [38], and constructing perturbatively a solution away from the near-horizon region [37].…”

Section: Discussionmentioning

confidence: 99%

Blandford--Znajek monopole expansion revisited: novel non-analytic contributions to the power emission

Camilloni¹,

Dias²,

Grignani³

et al. 2022

Preprint

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The Blandford and Znajek (BZ) split-monopole serves as an important theoretical example of the mechanism that can drive the electromagnetic extraction of energy from Kerr black holes. It is constructed as a perturbative low spin solution of Force Free Electrodynamics (FFE). Recently, Armas et al. put this construction on a firmer footing by clearing up issues with apparent divergent asymptotics. This was accomplished by resolving the behavior around the outer light surface, a critical surface of the FFE equations. Building on this, we revisit the BZ perturbative expansion, and extend the perturbative approach to higher orders in the spin parameter of the Kerr black hole. We employ matchedasymptotic-expansions and semi-analytic techniques to extend the split-monopole solution to the sixth-order in perturbation theory. The expansion necessarily includes novel logarithmic contributions in the spin parameter. We show that these higher order terms result in non-analytic contributions to the power and angular momentum output. In particular, we compute for the first time the perturbative contributions to the energy extraction at seventh-and eighth-order in the spin parameter. The resulting formula for the energy extraction improves the agreement with numerical simulations at finite spin. Moreover, we present a novel numerical procedure for resolving the FFE equations across the outer light surface, resulting in significantly faster convergence and greater accuracy, and extend this to higher orders as well. Finally, we include a general discussion of light surfaces as critical surfaces of the FFE equations.

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Section: Discussionmentioning

confidence: 99%

Blandford--Znajek monopole expansion revisited: novel non-analytic contributions to the power emission

Camilloni¹,

Dias²,

Grignani³

et al. 2022

Preprint

Self Cite

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“…In this paper, following the approach introduced in our letter [34], we have proposed a perturbative procedure to construct stationary, axisymmetric, FF magnetospheres around extreme Kerr black holes that are magnetically-dominated. Our approach, as well as the results in this paper, are analytical; however, as already discussed in the introduction, it would be interesting to numerically implement the perturbative algorithm to higher orders.…”

Section: Discussionmentioning

confidence: 99%

“…Our goal with this paper is to implement the new strategy proposed in our letter [34] for finding magnetically-dominated FF magnetospheres in the background of extreme Kerr, in which J = M 2 , where J is the angular momentum and M is the mass of the black hole. This choice is motivated by the observational evidence that nearly extreme black holes exist in nature [35][36][37][38][39].…”

Section: Introduction and Outlinementioning

confidence: 99%

“…For this reason, in this paper, we will take advantage of the attractor solution to construct perturbative solutions to FFE around it. As proposed in our letter [34], the strategy that we follow is to move away from the throat in the NHEK geometry towards extreme Kerr, with the aim of finding, at the second order in a suitable expansion parameter, a perturbative magnetically-dominated solution to FFE in the extreme Kerr background.…”

Section: Introduction and Outlinementioning

confidence: 99%

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Moving away from the Near-Horizon Attractor of the Extreme Kerr Force-Free Magnetosphere

Camilloni,

Grignani,

Harmark

et al. 2020

Preprint

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We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is no known exact analytic solution to force free electrodynamics which is stationary, axisymmetric and magnetically-dominated. However, any stationary, axisymmetric and regular force-free magnetosphere in extreme Kerr black hole approaches the same attractor solution in the near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show that by moving away from the attractor solution in the NHEK region, one finds magnetically-dominated solutions in the extreme Kerr black hole with finite and negative angular momentum outflow. This result is achieved using a perturbative analysis up to the second order.

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“…Theoretically, as the first step, one has to understand clearly the photon emissions around the black hole, especially near the black hole horizon. On the other hand, studying the photon emissions from the near-horizon area is important to explore various high-energy processes [16][17][18][19][20][21][22][23][24][25][26] happened in the near-horizon region (inside the ergosphere).…”

Section: Introductionmentioning

confidence: 99%

Photon emissions from near-horizon extremal and near-extremal Kerr equatorial emitters

Yan,

Hu,

Guo

et al. 2021

Preprint

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We consider isotropic and monochromatic photon emissions from equatorial emitters moving along future-directed timelike geodesics in the near-horizon extremal Kerr (NHEK) and near-horizon near-extremal Kerr (near-NHEK) regions, to asymptotic infinity. We obtain numerical results for the photon escaping probability (PEP) and derive analytical expressions for the maximum observable blueshift (MOB) of the escaping photons, both depending on the emission radius and the emitter's proper motion. In particular, we find that for all anti-plunging or deflecting emitters that can eventually reach to asymptotic infinity, the PEP is greater than 50% while for all plunging emitters the PEP is less than 55%, and for the bounded emitters in the (near-)NHEK region, the PEP is always less than 59%. In addition, for the emitters on unstable circular orbits in the near-NHEK region, the PEP decreases from 55% to 50% as the orbital radius decreases from the one of the innermost stable circular orbit to the one of the horizon. Furthermore, we show how the orientation of the emitter's motion along the radial or azimuthal direction affects the PEP and the MOB of the emitted photons.

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Force-free magnetosphere attractors for near-horizon extreme and near-extreme limits of Kerr black hole

Cited by 8 publications

References 30 publications

Blandford--Znajek monopole expansion revisited: novel non-analytic contributions to the power emission

Blandford--Znajek monopole expansion revisited: novel non-analytic contributions to the power emission

Moving away from the Near-Horizon Attractor of the Extreme Kerr Force-Free Magnetosphere

Photon emissions from near-horizon extremal and near-extremal Kerr equatorial emitters

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