Accretion Disk — Compact-Object Astrophysics in 60 Seconds #Shorts

Hinzugefügt: 2026-05-16

[00:00:00]Quasars outshine entire galaxies and the engine is no bigger than our solar system. The trick is feeding gas into a black hole the right way. An accretion disk is a flattened ring of gas spiraling toward a compact object.

[00:00:11]Friction between layers heats the gas to millions of degrees while it slowly drifts inward. Each ring obeys Kepler's third law. Orbital speed scales as one over the square root of radius. Inner gas laps outer gas, shearing and heating in the process. Temperature rises sharply as you approach the center. The effective temperature falls as radius to the minus three-quarters power, so the inside glows in x-rays. The disk truncates at the innermost stable circular orbit, six gravitational radii for a non-spinning black hole. Inside that, gas plunges in roughly a free-fall time. Magneto-rotational instability turns weak fields into turbulent stresses, the alpha viscosity. That viscosity is what actually drains angular momentum and lets gas accrete.

[00:00:53]About 1/10 of the rest mass energy escapes as radiation before crossing the horizon. That is roughly 20 times more efficient than hydrogen fusion in stars.

[00:01:02]Strong gravity bends photons around the hole, so the back of the disk reappears above and below the foreground, the warped silhouette imaged by Event Horizon Telescope. If a black hole spins fast enough, the ISCO shrinks to one gravitational radius and efficiency reaches 42%. Could a maximally rotating Kerr disk power a flare we have already missed?