What distinguishes a quiescent black hole from an active galactic nucleus (AGN)?

• A. Quiescent BH emits strong broad-band emission; AGN is faint.
• B. Quiescent BH accretes rapidly; AGN accretes slowly.
• C. Quiescent BH does not exist; all black holes are AGN.
• D. An AGN has high accretion rates and bright emission across bands due to the accretion disk and jets.

Answer: (D)

The main idea is that a black hole’s activity is set by how much matter it’s currently swallowing, which powers its light output. A quiescent black hole is feeding at a very low rate, so it shines feebly across the spectrum and shows little sign of a hot disk or jets. In contrast, an active galactic nucleus is a supermassive black hole that is rapidly accreting, and that intense inflow heats the inner disk and drives energetic processes like corona emission and relativistic jets. That combination produces bright, multiwavelength emission—from optical/UV through X-rays and often radio—that you can actually observe. So the defining distinction is high accretion rates leading to bright, broad-band emission due to the accretion disk and jets, which is exactly what the described option states.