Question

Why wouldn't an accretion disk orbiting a giant star get as hot as an accretion disk orbiting a compact object?

Answer 1

Answer:

The particles in an accretion disc around a small compact object are moving faster and have more energy.

Explanation:

As with anything orbiting around body, the smaller the orbit the faster the object travels. Particles in an accretion disc around a large star will be travelling relatively slowly

Particles in an accretion disc around a compact objects will be travelling much faster. As a result collisions between particles will have more energy and will generate more heat. Also, gravitational effects from the compact body will provide additional heating effects.