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

Answer 1

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

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

Because of their increased speed, particles in an accretion disc surrounding a compact object will collide with more energy and produce more heat; additionally, the compact body's gravitational pull will cause additional heating effects.

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Answer 2

Nova Adams

Because the compact object's stronger gravitational field causes greater compression and heating of the infalling material, an accretion disk orbiting a giant star would not get as hot as one orbiting the latter due to the lower gravitational potential energy released during accretion.

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Answer from HIX Tutor

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