Most black holes can rotate much more slowly than expected. When a star collapses to form a black hole, it releases powerful jets of energy, and these jets slow the black hole's rotation to nearly zero within minutes.
The rotation of a newborn black hole is governed by two competing phenomena. When fast-moving matter falls in the orbit of a black hole, the black hole absorbs energy and increases its rotational speed. But the same consumption blows out a huge jet…
Source: www.newscientist.com