Tests of Loop Quantum Gravity from the Event Horizon Telescope Results of Sgr A*

Abstract

The Event Horizon Telescope (EHT) collaboration’s image of the compact object at the Galactic center is the first direct evidence of the supermassive black hole (BH) Sgr A*. The shadow of Sgr A* has an angular diameter d sh = 48.7 ± 7 μas with fractional deviation from the Schwarzschild BH shadow diameter δ = − 0.08 − 0.09 + 0.09 , − 0.04 − 0.10 + 0.09 (for the VLTI and Keck mass-to-distance ratios). Sgr A*'s shadow size is within 10% of Kerr predictions, equipping us with yet another tool to analyze gravity in the strong-field regime, including testing loop quantum gravity (LQG). We use Sgr A*'s shadow to constrain the metrics of two well-motivated LQG-inspired rotating BH (LIRBH) models characterized by an additional deviation parameter L q , which recover the Kerr spacetime in the absence of quantum effects (L q → 0). When increasing the quantum effects through L q , the shadow size increases monotonically, while the shape gets more distorted, allowing us to constrain the fundamental parameter L q . We use the astrophysical observables shadow area A and oblateness D to estimate the BH parameters. It may be useful in extracting additional information about LIRBHs. While the EHT observational results completely rule out the wormhole region in LIRBH-2, a substantial parameter region of the generic BHs in both models agrees with the EHT results. We find that the upper bounds on L q obtained from the shadow of Sgr A*—L q ≲ 0.0423 and L q ≲ 0.0821 for the two LIRBHs, respectively—are more stringent than those obtained from the EHT image of M87*.

Shadows of loop quantum black holes: semi-analytical simulations of loop quantum gravity effects on Sagittarius A* and M87*

“…By comparing with EHT observations [67][68][69][70][71][72], we can constrain the value of polymeric function P in LQG. Although analytical calculations [36,87] can determine the shadow silhouette cast, in reality, the accretion disk produces extended emission around the photon ring, which significantly alters the shadow morphology. The impact of plasma and metric on the BH images was investigated earlier [88,89], which shows the size of the luminous ring is greatly influenced by both of them.…”

“…Considering that dimensionless spin a is also proportional to the gravitational constant, which also needs to be scaled by a factor of (1 + P ) 2 /(1 − P ) 2 . We should note that [87] uses the gravitational constant G LQG rather than the Newtonian gravitational constant G N in their comparison between the shadow image data and LQBH with different polymeric functions. Therefore, the result of our work is expected to be different from [87].…”

“…We should note that [87] uses the gravitational constant G LQG rather than the Newtonian gravitational constant G N in their comparison between the shadow image data and LQBH with different polymeric functions. Therefore, the result of our work is expected to be different from [87].…”

Online Classes During COVID-19 Period: A Study of Students’ Experience at Jamia Millia Islamia, New Delhi, India

“…The boundary of the shadow is determined by the photon ring, which principally relies on the black hole's parameters [68]. The application of the shadow in understanding near-horizon geometry has sparked a flurry of activity in analyzing, both analytically and numerically, shadows for black holes in GR [12,34, and in LQG [53,54,[91][92][93]. The EHT observation unveiled the shadows of supermassive black holes Sgr A* and M87* [1,94] whose sizes are within 10 percent of the Kerr predictions, furnishing another tool to explore the nature of strong-field gravity.…”

Exploring the shadow of a rotating charged ModMax black hole

“…Theoretical studies of BH shadows for different gravity models and BH solutions can be found in . After the first ever observation of the BH shadows of M87 and Sgr A * in 2019 [19] and in 2022 [21], the observations have been developed by various authors [91][92][93][94][95][96][97][98].…”