active-galactic-nuclei

Active galactic nuclei are galaxy cores lit up by supermassive black holes pulling in gas. Quasars, Seyfert galaxies, radio galaxies, and blazars are largely one machine seen from different angles and at different power.

Quasars outshine entire galaxies from a region smaller than the solar system. They powered the early universe, shaped galaxy formation, and are now our most powerful probes of cosmic history. Here's what they actually are.