---
title: "How accretion disks shine"
description: "Follow gas from angular-momentum transfer to disk heating and thermal spectra, then compare how the emitted light reaches a distant observer."
canonical_url: "https://sandboxphysics.com/stories/accretion-disks/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/accretion-disks/"
last_modified: "2026-11-13"
---

Astronomy reading

# How accretion disks shine

Sandbox Physics · 2026-11-12

Begin with two rings pulling on each other. Follow the energy that heats the gas, add radiation from rings at different temperatures, and see how motion and gravity change the light received far away.

1. L1 · Concept

   ## [Why gas around a black hole shines](https://sandboxphysics.com/stories/accretion-disks/why-accretion-disks-shine/)

   Orbiting gas gives angular momentum outward and settles inward. The difference in orbital energy heats the disk and powers its radiation.

2. L2 · Chapter

   ## [Where a thin disk heats](https://sandboxphysics.com/stories/accretion-disks/thin-disk-torque-temperature/)

   Derive a thin disk’s surface flux from torque work, locate its hottest ring and calculate the luminosity of both disk faces.

3. L2 · Chapter

   ## [Adding the spectra of differently heated rings](https://sandboxphysics.com/stories/accretion-disks/adding-disk-blackbody-spectra/)

   Add diluted Planck emission from disk annuli, distinguish intensity from flux, and predict how a hotter disk changes its spectrum.

4. L3 · Chapter

   ## [How frequency and brightness change on the way out](https://sandboxphysics.com/stories/accretion-disks/photon-frequency-and-brightness/)

   Follow one light path from disk to observer, derive the cubic and fourth-power intensity factors, and separate frequency shift from heating.

5. L3 · Chapter

   ## [Which disk surface a light path meets first](https://sandboxphysics.com/stories/accretion-disks/first-opaque-disk-crossing/)

   Trace a saved path through an inner hole to its first opaque disk encounter, and distinguish known darkness from unresolved critical paths.

6. L4 · Method and paper reading

   ## [Recompute a disk image and spectrum from saved intersections](https://sandboxphysics.com/stories/accretion-disks/recompute-frozen-disk-light/)

   Follow one frozen disk intersection through thermal emission, a finite image cell and the full spectrum with a portable Python tutorial.

7. L4 · Method and paper reading

   ## [How to read a thin-disk spectrum paper](https://sandboxphysics.com/stories/accretion-disks/reading-thin-disk-spectrum-paper/)

   Read the axes, caption and assumptions of a Kerr disk spectrum figure, then identify the external inputs needed for a spin estimate.