Accretion Disk
A rotating disk structure formed by infalling diffuse matter orbiting a massive central body like a white dwarf, neutron star, or black hole.
Governing formula
L_acc = η M_dot c² (Efficiency η ~ 0.1 to 0.42)
SI unit
Watts or Solar Luminosity
In depth
Viscous friction and differential rotation in the disk convert gravitational potential energy into intense thermal radiation, achieving up to 42% mass-to-energy conversion efficiency (far higher than nuclear fusion at 0.7%).
Examples in the real world
The superheated glowing accretion disk surrounding supermassive black hole M87* imaged by the Event Horizon Telescope.