A black hole mimicker hiding in the shadow: Optical properties of the $gamma$ metric. (arXiv:1904.06207v1 [gr-qc])
<a href="http://arxiv.org/find/gr-qc/1/au:+Abdikamalov_A/0/1/0/all/0/1">Askar B. Abdikamalov</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Abdujabbarov_A/0/1/0/all/0/1">Ahmadjon A. Abdujabbarov</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Malafarina_D/0/1/0/all/0/1">Daniele Malafarina</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Bambi_C/0/1/0/all/0/1">Cosimo Bambi</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Ahmedov_B/0/1/0/all/0/1">Bobomurat Ahmedov</a>
Can the observation of the “shadow” allow us to distinguish a black hole from
a more exotic compact object? We study the motion of photons in a class of
vacuum static axially-symmetric space-times that is continuously linked to the
Schwarzschild metric through the value of one parameter that can be interpreted
as a measure of the deformation of the source. The analysis of the effective
potential of the radial motion of massless particles shows that there are three
distinguishable range for $gamma$: i) $gamma<1/sqrt{5}$; ii) $1/sqrt{5}
leq gamma < 1/2$; iii) $gamma> 1/2$. We investigate the lensing effect and
shadow produced by the source with the aim of comparing the expected image with
the shadow of a Schwarzschild black hole. In the context of astrophysical black
holes we found that it may not be possible to distinguish an exotic source with
small deformation parameter from a black hole. However, as the deformation
increases noticeable effects arise. Therefore, the measurement of the shadow of
astrophysical black hole candidates would in principle allow to put constraints
on the deviation of the object from spherical symmetry.
Can the observation of the “shadow” allow us to distinguish a black hole from
a more exotic compact object? We study the motion of photons in a class of
vacuum static axially-symmetric space-times that is continuously linked to the
Schwarzschild metric through the value of one parameter that can be interpreted
as a measure of the deformation of the source. The analysis of the effective
potential of the radial motion of massless particles shows that there are three
distinguishable range for $gamma$: i) $gamma<1/sqrt{5}$; ii) $1/sqrt{5}
leq gamma < 1/2$; iii) $gamma> 1/2$. We investigate the lensing effect and
shadow produced by the source with the aim of comparing the expected image with
the shadow of a Schwarzschild black hole. In the context of astrophysical black
holes we found that it may not be possible to distinguish an exotic source with
small deformation parameter from a black hole. However, as the deformation
increases noticeable effects arise. Therefore, the measurement of the shadow of
astrophysical black hole candidates would in principle allow to put constraints
on the deviation of the object from spherical symmetry.
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