Comment by whatshisface

Disks minimize gravitational potential energy when angular momentum is held constant. Forming solar systems have ways of radiating energy, but they can't really radiate angular momentum. That's why galaxies and solar systems tend to be disk-shaped. The disk shape is very general and comes from fundamental principles, so I don't see why it couldn't continue to apply when one bit of mass in the system just so happens to be a black hole.