According to the “no-hair theorem” of general relativity, static...
According to the “no-hair theorem” of general relativity, static and isolated black holes can be fully characterized by just two numbers, the mass (M) and the angular momentum (J). Norman Gürlebeck has now shown that, under certain assumptions, the no-hair theorem is still valid when the black hole is not isolated but, for instance, surrounded by a matter disk.
Via APS Physics: The Simplicity of Black Holes. [By the way, congrats for the new look they have changed for the better]