Rotating black holes are made gravitational collapse of a super heavy spinning star or from the collapse or collision of a lot of compact objects, stars, or gases that spin. As every known star rotates and real collisions have an angular momentum that is not zero, it is thought that all black holes in nature are rotating black holes. [3][1]
In late 2006, astronomers wrote about the spin rates of black holes people know of in The Astrophysical Journal. A black hole in the Milky Way, GRS 1915+105, may rotate 1,150 times per second, which is almost as fast as what astronomers think is the fastest any black hole can rotate. [4]