**Publication date:** Jul 2014

**Abstract:**

We discuss photon and test-particle orbits in the Kehagias-Sfetsos (KS)

metric of Hořava’s gravity. For any value of the Hořava parameter ω,

there are values of the gravitational mass M for which the metric

describes a naked singularity, and this is always accompanied by a

vacuum „antigravity sphere“ on whose surface a test particle can remain

at rest (in a zero angular momentum geodesic), and inside which no

circular geodesics exist. The observational appearance of an accreting

KS naked singularity in a binary system would be that of a quasistatic

spherical fluid shell surrounded by an accretion disk, whose properties

depend on the value of M, but are always very different from accretion

disks familiar from the Kerr-metric solutions. The properties of the

corresponding circular orbits are qualitatively similar to those of the

Reissner-Nordström naked singularities. When event horizons are present,

the orbits outside the Kehagias-Sfetsos black hole are qualitatively

similar to those of the Schwarzschild metric.

**Authors:**

Vieira, Ronaldo S. S.; Schee, Jan; Kluźniak, Włodek; Stuchlík, Zdeněk; Abramowicz, Marek;