Why do astronomers believe that the engine at the center of a quasar is a supermassive black hole?

Question

Olivia Aldridge · Accepted Answer

Quasars are small and emit such huge amounts of energy that a supermassive black hole is the best known explanation of their power source.

A supernova explosion can release enormous amounts of energy, but only for a few weeks at a time; quasars release energy for extended periods of time. The energy output of quasars varies over timescales of days or months, indicating that the energy source must be relatively small, on the order of our solar system's size. Supermassive black holes, which are found at the centers of many galaxies, including our own, are thought to be at the center of every galaxy and are responsible for the galaxy's evolution. An accretion disc is a region of material that falls into a supermassive black hole. If a large amount of material falls into the disc, friction and gravitational forces cause it to heat up to a point where it releases enormous amounts of energy, which is known as a quasar.

Hazel Asher · Answer

undefined Because of a number of factors, astronomers believe that the engine at the center of a quasar is a supermassive black hole: 1. **High Luminosity:** Quasars are extremely bright and emit vast amounts of energy, indicating a highly energetic process; 2. **Small Size:** Despite their luminosity, quasars are compact, suggesting that the energy source is concentrated in a small volume; 3. **Rapid Variability:** Quasars exhibit rapid changes in brightness over short periods of time, which suggests a compact and massive object causing the fluctuations; 4. **Broad Emission Lines:** Quasars display broad emission lines in their spectra, indicative of gas swirling around a massive object at high speeds, which is consistent with the behavior of matter around black holes; 5. **Absorption Lines:** Some quasars display