Evolution of Kerr superspinars due to accretion counterrotating thin discs

Abstract

Abstract The string theory predicts existence of extremely compact objects spinning faster than the Kerr black holes. The spacetime exterior to such superspinars is described by the Kerr naked singularity geometry breaking the black hole limit on the internal angular momentum. We demonstrate that conversion of Kerr superspinars into a near-extreme black hole due to an accretion counterrotating Keplerian disc is much more effective in comparison with the case of a corotating one since both the accreted rest mass necessary for conversion and the evolution time of conversion are by orders smaller for counterrotating discs. The conversion time of Kerr superspinars is given for several accretion regimes, and it is shown that the self-regulated accretion flow implies fastest evolution to the black-hole state. In final stages of the conversion, Kerr superspinars can serve as very efficient particle accelerators in the region where the black-hole horizon forms. 1 Introduction The string theory predicts a very interesting possibility to be tested in the framework of relativistic astrophysics. As shown by Gimon and Hořava [ 1 ], Kerr superspinars with mass M and angular momentum J violating the general relativistic bound on the spin of compact objects (a ≡ J/M 2 > 1) could be primordial remnants of the high-energy phase of very early period of the evolution of the Universe when the effects of the string theory were relevant. The spacetime outside a Kerr