Testing Strong Gravitational Lensing Effects of Supermassive Compact Objects with Regular Spacetimes
Year: 2022
Type: article
Abstract: We compare and contrast gravitational lensing, in the strong field limit, by the photon sphere in spherically symmetric regular electrically charged (REC) black holes (0 < b ≤ b E ) and with those by corresponding REC no-horizon spacetimes ( b > b E ). Here, b is an additional parameter due to the charge and the value b = b E ≈ 0.226 corresponds to an extremal black hole with degenerate horizons. Interestingly, the spacetime admits a photon sphere for 0 < b ≤ b P ≈ 0.247 and an anti-photon sphere only for b E < b ≤ b P . With no-horizon spacetime, images by lensing from the inside of the photon sphere ( u < u ps ) can also appear. Interestingly, for the case of u < u ps the deflection angle α D increases with u . We analyze the lensing observables by modeling compact objects Sgr A*, M87*, NGC 4649, and NGC 1332 as black holes and no-horizon spacetimes. The angular position θ ∞ and photon sphere radius x ps decrease with increasing parameter b . Our findings suggest that the angular separations ( s ) and magnification ( r ) of relativistic images inside the photon sphere may be higher than those outside. Moreover, the time delay for Sgr A* and M87* can reach ∼8.8809 and ∼12,701.8 minutes, respectively, at b = 0.2, deviating from Schwarzschild black holes by ∼2.615 and ∼4677 minutes. These deviations are insignificant for Sgr A* because it is too small, but they are sufficient for astronomical observation of M87* and some other black holes. With EHT bounds on the θ sh of Sgr A* and M87* within the 1 σ region, placing bounds on the parameter b , our analysis concludes that REC black holes agree with the EHT results in finite space, whereas the corresponding REC no-horizon spacetimes are completely ruled out.
Source: The Astrophysical Journal
Institutions: Jamia Millia Islamia, University of KwaZulu-Natal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W4306700073