Overspinning Kerr-MOG black holes by test fields and the third law of black hole dynamics

Abstract

We evaluate the stability of the event horizons of Kerr-MOG black holes in the scattering process of scalar test fields. We show that both extremal and nearly extremal Kerr-MOG black holes can be overspun into naked singularities by scalar test fields with a frequency slightly above the superradiance limit. The overspinning becomes generic as the the modification parameter α increases, i.e. the black holes are rendered more and more vulnerable against perturbations as the space-time deviates from the Kerr solution. We also show that nearly extremal Kerr-MOG black holes can be continuously driven to extremality. The third law of black hole dynamics is violated for any non-zero value of the modification parameter α.

Cosmic censorship, massless fermionic test fields, and absorption probabilities

“…The overspinning problem due to these modes can be fixed by backreaction effects which contribute to second order to Δ fin . In our previous analysis for Kerr-MOG [40], and Kerr-Newman black holes [62] we have verified that the overspinning of Kerr black holes by scalar fields is fixed by the backreaction effects. This relies on the fact that the superradiance limit prevents the absorption of modes with frequencies much smaller than ω crit .…”

“…In a seminal work by Will this increase in the angular velocity has been estimated as [65] ΔΩ = δ J 4M 3 (24) where δ J denotes the angular momentum of the test field. In our recent works [40,61] we argued that the induced increase in the angular velocity of the horizon leads to an increase in the superradiance limit for bosonic fields and prevents the absorption of the challenging modes. The induced increase in the angular velocity also induces a first order correction in the self-energy of the test field.…”

“…Following Wald various thought experiments were constructed to test the validity of cosmic censorship. These thought experiments involve perturbations of the black holes with both test particles , and fields [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. There were also attempts to incorporate quantum effects [44][45][46][47][48][49][50], and test the validity of cosmic censorship for asymptotically anti-de Sitter cases [51][52][53][54][55][56][57][58].…”

Destroying Kaluza-Klein and Kerr-Newman black holes

“…The similar idea to Hubeny's in violating WCCC for Kerr black hole was proposed Jacobson and Sotiriou [9], for Kerr-Newman black hole were discussed in [10,11], and for magnetized Kerr black hole is investigated in [12]. The reconsideration of WCCC in the fashion of Hubeny [8] is not limited just to black holes in Einstein-Maxwell theory, but also beyond [13,14,15,16,17,18,19,20]. However, a newer version of checking WCCC by Sorce and Wald [21] shows that if the self-force and finite size effects are considered, then no such black hole destruction as illustrated in [8,9,11,12] can occur.…”

“…We show that, with the help of numerical results, both black holes can be destroyed by letting them capture test object from far away. Indeed, similar to the presentations in [11,33,12,10,14,13], here we neglect the self-energy or backreaction factors which recently were used by some authors in proving the WCCC violation proposed in [8,9]. For Kaluza-Klein black hole discussion, we also add an analysis on the naked singularity production by considering the neutral scalar field absorption which leads to an overspinning of the black hole.…”