Zdeněk StuchlíkJan Schee;


Kerr superspinning geometry with dimensionless spin a>1 can describe exterior of primordial superspinars, extremely compact and massive objects indicated by String Theory. Accretion have to convert them into near-extreme Kerr black holes, but they could survive to the era of high-redshift quasars. However, superspinning objects could arise also from gravitational collapse.

There is a variety of unexpected physical phenomena related to the Kerr superspinning geometry enabling to distinguish them from Kerr black holes. In the final stages of the conversion of a near-extreme Kerr superspinar, the efficiency of Keplerian accretion increases up to 157.7%, much larger than the 42.3% that is the limit value for Kerr black holes. Some optical phenomena give signatures enabling a clear distinction between the Kerr superspinars and Kerr black holes even on the cosmologically large distances, namely the shape and extension of profiled spectral lines generated in the innermost parts of accretion discs. For Kerr superspinning objects located close enough, their silhoutte can be observed that is substantially different from the Kerr black hole silhuette, and the optical appearance of the Keplerian disc can be strongly modified in comparison to those occuring around the Kerr black holes.

In the deep gravitational field of near-extreme Kerr superspinars, ultra-high-energy processes can occur with no fine tuning of the motion constants of the colliding particles, and the products of the collisions can escape to infinity with the directional and energetical efficiency much larger than in the case of collisions in vicinity of the horizon of near-extreme Kerr black holes. For this large efficiency of ultra-high-energy collisions related to the distant observers, both non-existence of the event horizon, and the strong rotational effect are relevant. In fact, the study of the high-energy collisions in the field of the spherically symmetric static Kehagias-Sfetsos naked singularity solutions of the Hořava gravity indicates clearly that the efficiency of the collisions, related to the distant observers, is substantially reduced due to the gravitational redshift effect and the energy escaping to infinity corresponds to the rest mass (covariant energy) of the colliding particles. This indicates the crucial role of the rotational phenomena, energy much larger than the covariant energy of the colliding particles can be measured by the distant observers.

The extraordinary phemonema occuring in the Kerr superspinning geometry could be observed by some of the sophisticated satellite observatories under preparation, as the LOFT or ATHENA are, giving thus potentially an observational support for ideas of String Theory.