Publication date: Dec 2015
Abstract:
In this paper, we study circular geodesic motion of test particles and
photons in the Bardeen and Ayon-Beato-Garcia (ABG) geometry describing
spherically symmetric regular black-hole or no-horizon spacetimes. While
the Bardeen geometry is not exact solution of Einstein’s equations, the
ABG spacetime is related to self-gravitating charged sources governed by
Einstein’s gravity and nonlinear electrodynamics. They both are
characterized by the mass parameter m and the charge parameter g. We
demonstrate that in similarity to the Reissner-Nordstrom (RN) naked
singularity spacetimes an antigravity static sphere should exist in all
the no-horizon Bardeen and ABG solutions that can be surrounded by a
Keplerian accretion disc. However, contrary to the RN naked singularity
spacetimes, the ABG no-horizon spacetimes with parameter g/m > 2 can
contain also an additional inner Keplerian disc hidden under the static
antigravity sphere. Properties of the geodesic structure are reflected
by simple observationally relevant optical phenomena. We give silhouette
of the regular black-hole and no-horizon spacetimes, and profiled
spectral lines generated by Keplerian rings radiating at a fixed
frequency and located in strong gravity region at or nearby the
marginally stable circular geodesics. We demonstrate that the profiled
spectral lines related to the regular black-holes are qualitatively
similar to those of the Schwarzschild black-holes, giving only small
quantitative differences. On the other hand, the regular no-horizon
spacetimes give clear qualitative signatures of their presence while
compared to the Schwarschild spacetimes. Moreover, it is possible to
distinguish the Bardeen and ABG no-horizon spacetimes, if the
inclination angle to the observer is known.
Authors:
Stuchlík, Zdeněk; Schee, Jan;