Constraining rotating black hole via curvature radius with observations of M87*

Understand

Combined with the observation of M87*, shadow has gradually became a promising test of the black hole nature.

• Recently, EHT collaboration gave new constraints on the shadow size at 68\% confidence levels.
• In this work, we consider the new constrains on the black hole spin and charge for the Kerr and Kerr-Newmann black holes via the local curvature radius.
• For the Kerr black holes, the cases with high spin and large inclination angle are ruled out.