What disk of hot matter can form as gas spirals into a black hole?

The disk of hot matter that can form as gas spirals into a black hole is an accretion disk.

Gas rarely falls straight into a black hole because it usually carries angular momentum. Instead, the material spreads into a rapidly rotating, flattened structure. Collisions, turbulence, magnetic effects, and friction transfer angular momentum outward, allowing some gas to spiral inward.

As the gas moves deeper into the black hole’s gravitational well, gravitational potential energy is converted into heat and radiation. The inner regions can become extremely hot and shine strongly in ultraviolet or X-rays. This glowing disk often lets astronomers detect a black hole indirectly, since the black hole itself emits no ordinary light from inside its event horizon.

An accretion disk is not the same as a protoplanetary disk, although both are disks of orbiting material. A galactic disk is the much larger, star-filled structure of a galaxy. Accretion disks also occur around young stars, white dwarfs, and neutron stars, not only black holes. In some black-hole systems, powerful jets emerge along the object’s rotational axis.