Astrophysical Violations of the Kerr Bound as a Possible Signature of String Theory

TL;DR

This paper proposes that string theory allows for violations of the Kerr bound, leading to superspinars that could produce highly efficient energy transfer, potentially serving as observable signatures supporting string theory.

Contribution

It introduces the concept that string theory permits black-hole-like objects to spin faster than the Kerr limit, which could be detected through astrophysical observations.

Findings

Superspinars can spin faster than Kerr black holes.

Energy transfer efficiency can reach 100% near superspinars.

Potential observational signatures include active galactic nuclei and gamma-ray bursts.

Abstract

In 4D general relativity, the angular momentum of a black hole is limited by the Kerr bound. We suggest that in string theory, this bound can be breached and compact black-hole-like objects can spin faster. Near such "superspinars," the efficiency of energy transfer from the accreting matter to radiation can reach 100%, compared to the maximum efficiency of 42% of the extremal Kerr (or 6% of the Schwarzschild) black hole. Finding such superspinning objects as active galactic nuclei, GBHCs, or sources of gamma ray bursts, could be viewed as experimental support for string theory.