https://phys.org/news/2019-01-black-hole-galaxy-rapidly.html

Using observations from state-of-the-art technology, the team of researchers found evidence that a stellar-mass black hole in our galaxy (known as 4U 1630-472) is rotating rapidly (at a speed of 92-95 per cent of the theoretically-allowed rotational speed) around its axis while sucking in falling material. It is subject to gravitational stresses and temperatures so high that it begins to shine brightly in X-rays, which were seen by astronomers using telescopes.

According to Einstein's General Theory of Relativity (GR), if a black hole is rotating rapidly, then it will modify the space and time around it in a way which is different than that for a black hole which is not rotating.