Shadows of spherically symmetric black holes and naked singularities

@article{Shaikh2018ShadowsOS,
  title={Shadows of spherically symmetric black holes and naked singularities},
  author={Rajibul Shaikh and Prashant Kocherlakota and Ramesh Narayan and Pankaj S. Joshi},
  journal={Monthly Notices of the Royal Astronomical Society},
  year={2018}
}
We compare shadows cast by Schwarzschild black holes with those produced by two classes of naked singularities that result from gravitational collapse of spherically symmetric matter. The latter models consist of an interior naked singularity space–time restricted to radii r ≤ R_b, matched to Schwarzschild space–time outside the boundary radius R_b. While a black hole always has a photon sphere and always casts a shadow, we find that the naked singularity models have photon spheres only if a… 

Figures from this paper

Shadow of a naked singularity without photon sphere
It is generally believed that the shadows of either a black hole or naked singularity arise due to photon spheres developing in these spacetimes. Here we propose a new spherically symmetric naked
Shadow of nulllike and timelike naked singularities without photon spheres
In this paper, we derive general conditions for a shadow to occur, without a photon sphere in a spacetime, caused by central nulllike or timelike naked singularities. Using these conditions, we
Can we distinguish black holes from naked singularities by the images of their accretion disks?
We study here images of thin accretion disks around black holes and two classes of naked singularity spacetimes and compare these scenarios. The naked singularity models which have photon spheres
Perihelion precession and shadows near black holes and naked singularities
It is now known that, apart from black holes, some naked singularities can also cast shadows which provide their possible observable signatures. We examine the relevant question here as to how to
Geodesic motion near self-gravitating scalar field configurations
TLDR
It turns out that a scalar field black hole has the innermost stable circular orbit and the (unstable) photon sphere, but their radii are always less than the corresponding ones for the Schwarzschild black hole of the same mass; moreover, these radii can be arbitrarily small.
Shadows and negative precession in non-Kerr spacetime
It is now known that the shadow is not only the property of a black hole, it can also be cast by other compact objects like naked singularities. However, there exist some novel features of the shadow
Photon ring structure of rotating regular black holes and no-horizon spacetimes
The Kerr black holes possess a photon region with prograde and retrograde orbits radii, respectively, M⩽rp−⩽3M and 3M⩽rp+⩽4M , and thereby always cast a closed photon ring or a shadow silhouette for
Distinguishing Brans–Dicke–Kerr type naked singularities and black holes with their thin disk electromagnetic radiation properties
The possible existence of naked singularities, hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon is still an open problem in present day
Observational signatures of strongly naked singularities: image of the thin accretion disk
We study the optical appearance of a thin accretion disk around the strongly naked static Janis-Newman-Winicour singularity. The solution does not possess a photon sphere, which results in the
Shadows around the q-metric
One crucial problem in relativistic astrophysics is that of the nature of black hole candidates. It is usually assumed that astrophysical black holes are described by the Schwarzschild or Kerr
...
...

References

SHOWING 1-10 OF 71 REFERENCES
Gravitational lensing by naked singularities
We model massive dark objects in galactic nuclei as spherically symmetric static naked singularities in the Einstein massless scalar field theory and study the resulting gravitational lensing in
Can strong gravitational lensing distinguish naked singularities from black holes
In this paper we study gravitational lensing in the strong field limit from the perspective of cosmic censorship, to investigate whether or not naked singularities, if at all they exist in nature,
Distinguishing black holes from naked singularities through their accretion disc properties
We show that, in principle, a slowly evolving gravitationally collapsing perfect fluid cloud can asymptotically settle to a static spherically symmetric equilibrium configuration with a naked
Spherical polytropic balls cannot mimic black holes
The so-called black hole shadow is a dark region which is expected to appear in a fine image of optical observation of black holes. It is essentially an absorption cross section of black hole, and
Time delay and magnification centroid due to gravitational lensing by black holes and naked singularities
We model the massive dark object at the center of the Galaxy as a Schwarzschild black hole as well as Janis-Newman-Winicour naked singularities, characterized by the mass and scalar charge
Shadow of a naked singularity
We analyze the redshift suffered by photons originating from an external source, traversing a collapsing dust cloud and finally being received by an asymptotic observer. In addition, we study the
Binary black hole shadows, chaotic scattering and the Cantor set
We investigate the qualitative features of binary black hole shadows using the model of two extremally charged black holes in static equilibrium (a Majumdar–Papapetrou solution). Our perspective is
Gravastar Shadows
Direct observation of black holes is one of the grand challenges in astronomy. If there are supercompact objects which possess unstable circular orbits of photons, however, it may be difficult to
TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. II. BLACK HOLE IMAGES
According to the no-hair theorem, all astrophysical black holes are fully described by their masses and spins. This theorem can be tested observationally by measuring (at least) three different
How does a naked singularity look
There are nonradial null geodesics emanating from the shell focusing singularity formed at the symmetric center in a spherically symmetric dust collapse. In this article, assuming self-similarity in
...
...