Testing Rotating Regular Metrics with EHT Results of Sgr A

The Event Horizon Telescope (EHT) observation unveiled the first image of supermassive black hole Sgr A* showing a shadow of diameter theta(sh)= 48.7 +/- 7 mu as with fractional deviation from the Schwarzschild black hole shadow diameter delta =-0.08(-0.09)(+0.09)(VLTI), -0.04(-0.10)(+0.09)(Keck). The Sgr A* shadow size is within 10% of the Kerr predictions, providing us with another tool to investigate the nature of strong-field gravity. We use the Sgr A* shadow observables to constrain metrics of four independent and well-motivated, parametrically different from Kerr spacetime, rotating regular spacetimes and the corresponding no-horizon spacetimes. We present constraints on the deviation parameter g of rotating regular black holes. The shadow angular diameter theta sh within the 1a region places bounds on the parameters a and g. Together with EHT bounds on the theta sh and delta of Sgr A*, our analysis concludes that the three rotating regular black holes, i.e., Bardeen, Hayward, and Simpson-Visser black holes, and corresponding no-horizon spacetimes agree with the EHT results of Sgr A*. Thus, these three rotating regular spacetimes and Kerr black holes are indiscernible in some parameter space, and one cannot rule out the possibility of the former being strong candidates to be astrophysical black holes.

Automated summary

The observation from the Event Horizon Telescope (EHT) has revealed the first image of the supermassive black hole Sgr A*, showing a deviation from the predicted size and providing a new tool for investigating strong-field gravity. Through analyzing the observables of Sgr A*'s shadow, constraints are placed on different metrics of rotating regular black holes and corresponding no-horizon spacetimes. The results suggest that these rotating regular spacetimes and Kerr black holes are indistinguishable in certain parameter space.