Some black holes spin in the same direction as their surrounding disks, and these do not produce jets. In addition, backwards spinning black holes will evolve over time and spin the other way, producing a weaker and weaker jet until it shuts off altogether.
This scenario may explain why only 10% of active galaxies have radio jets, and how active galaxies evolve over time. Since these powerful blasts of material significantly affect the surrounding galaxy, and even galaxy cluster in some cases, this work fits into the larger picture.
It also reminds me of how the vast array of different types of active galaxies seen in optical and radio were unified into one model with a supermassive black hole just a couple of decades ago. Maybe we are on the verge of another such shift in our thinking about these cool and powerful objects!
Above artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets that are visible in the radio. Image credit: NASA/JPL-Caltech This research is available on Arxiv.