SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/astro-agn-accretion-light

Where does most visible AGN power originate?

It comes from hot material in the accretion flow outside the event horizon.

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  1. Inside the singularity
  2. In hot orbiting gas outside the horizon ✔
  3. From the black hole surface

Why: Gas in the accretion disk rubs, heats, and radiates before crossing the event horizon. The black hole itself has no glowing material surface.

Huh, didn't know that: AGN emission can extend from radio waves through visible light to X-rays.

The dad joke
The accretion disk glows because falling in is hard work.
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References

Answer: In hot orbiting gas outside the horizon. Gas in the accretion disk rubs, heats, and radiates before crossing the event horizon. The black hole itself has no glowing material surface.

  1. What Are Active Galactic Nuclei? science.nasa.gov/mission/webb/science-overview/science-explainers/what-are-active-galactic-nuclei
    The particles in these ever-rotating accretion disks periodically rub together, creating heat and light.
    Checked 2026-10-10.

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