The Kerr metric is an exact solution of the Einstein Field Equation of general relativity for the spacetime around a rotating mass.
Unlike other solutions, this is an exact solution that explains black holes very well. However, there are still two problems: mathematical division by zero at the singularity, and when viewing the black hole from infinite distance, The Kerr solution converges to Minkowski space. However, the universe is not Minkowski space but rather FLRW Metric space, and this discrepancy has been a known issue for a long time. In other words, this means that when mass and rotation disappear, the gravitational effects of the Kerr metric also disappear and spacetime becomes flat.
