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How does gas falling toward a supermassive black hole power a quasar?

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six quasar host galaxies — Quasar Six quasar host galaxies, as observed by the Hubble Space Telescope.
Shown are apparently normal, solitary galaxies (left), colliding galaxies (centre), and merging galaxies (right).

Quasars are powered by the gravitational accretion of matter onto a supermassive black hole located at the center of a galaxy.12

As gas falls toward the black hole, it possesses sufficient angular momentum to prevent a direct inward plunge, causing it to form a rapidly rotating accretion disk. Within this disk, the gas spirals inward as it loses energy and angular momentum due to viscosity and turbulence.2

This process converts gravitational potential energy into intense heat, causing the material to reach temperatures of up to several million kelvins. As a result, the disk radiates vast amounts of energy across the electromagnetic spectrum, from infrared to X-ray wavelengths. This luminosity is so immense that it can outshine the entire host galaxy. The rate of this accretion is governed by the Eddington limit, which balances the inward pull of gravity against the outward pressure generated by the intense radiation produced during the heating of the infalling gas.2341