**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;