Most newborn black holes spew gas so hard they almost stop spinning

Most black holes can spin much more slowly than expected. When black holes form from collapsing stars, they emit powerful jets of energy, and these jets slow down the black holes in minutes.

The spin of a newborn black hole is driven by two competing phenomena. When fast-moving material enters its orbit, the black hole absorbs energy and its rotation speeds up. But due to the same consumption, a huge jet explodes…