Static stable timelike circular orbits and Aschenbach effect in horizonless solutions of Einstein cubic gravity

TL;DR

This paper explores the existence of stable static and circular orbits in horizonless Einstein cubic gravity solutions, revealing unique orbital structures and the presence of the Aschenbach effect, with implications for accretion disk behavior.

Contribution

It demonstrates the existence of static stable timelike circular orbits and the Aschenbach effect in horizonless Einstein cubic gravity solutions, a novel feature in such spacetimes.

Findings

Stable static orbits exist where particles remain at rest relative to distant observers.

The Aschenbach effect causes non-monotonic orbital velocity dependence on radius.

Regions with stable circular orbits can be discontinuous, with particles near the center having energies greater than one.

Abstract

In the spacetime of horizonless compact objects described by Einsteinian cubic gravity (ECG), we demonstrate the existence of static stable timelike circular orbits on which massive particles remain at rest relative to distant observers. These static orbits are further identified as the innermost stable circular orbits (ISCOs) in this spacetime. If such static orbits form part of an accretion disk, they would give rise to a ring-like structure that is unaffected by Doppler shifts. Moreover, the Aschenbach effect is shown to be present: the orbital velocity of particles on timelike circular orbits, as measured by a zero angular momentum observer (ZAMO), displays a non-monotonic dependence on the radial coordinate. Additionally, the regions supporting stable circular orbits can be discontinuous, and particles on stable orbits near the center can possess specific energies greater than one ($E > 1$).