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

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jats:titleAbstract</jats:title> jats:pThe 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 jats:italicd</jats:italic> jats:subsh</jats:sub> = 48.7 ± 7 jats:italicμ</jats:italic>as with fractional deviation from the Schwarzschild BH shadow diameter jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:miδ</mml:mi> mml:mo=</mml:mo> mml:mo−</mml:mo> mml:msubsup mml:mrow mml:mn0.08</mml:mn> </mml:mrow> mml:mrow mml:mo−</mml:mo> mml:mn0.09</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn0.09</mml:mn> </mml:mrow> </mml:msubsup> mml:mo,</mml:mo> mml:mo−</mml:mo> mml:msubsup mml:mrow mml:mn0.04</mml:mn> </mml:mrow> mml:mrow mml:mo−</mml:mo> mml:mn0.10</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn0.09</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="" xlink:href="apjacb334ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (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 jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub>, which recover the Kerr spacetime in the absence of quantum effects (jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub> → 0). When increasing the quantum effects through jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub>, the shadow size increases monotonically, while the shape gets more distorted, allowing us to constrain the fundamental parameter jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub>. We use the astrophysical observables shadow area jats:italicA</jats:italic> and oblateness jats:italicD</jats:italic> 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 jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub> obtained from the shadow of Sgr A*—jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub> ≲ 0.0423 and jats:italicL</jats:italic> jats:sub jats:italicq</jats:italic> </jats:sub> ≲ 0.0821 for the two LIRBHs, respectively—are more stringent than those obtained from the EHT image of M87*.</jats:p>



5107 Particle and High Energy Physics, 51 Physical Sciences

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American Astronomical Society