Britannica
Sources used in this answer
How are quasars different from radio galaxies?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
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 and radio galaxies are both types of active galactic nuclei (AGN) powered by the accretion of matter onto a central supermassive black hole. While they share this fundamental energy mechanism, they differ primarily in their observed luminosity and appearance.123
- Luminosity and Visibility: Quasars are among the most luminous objects in the universe, often outshining all the stars in their host galaxies. Because their central nuclei are so brilliant, the surrounding galaxy is frequently obscured, making the quasar appear as a small, starlike point of light. In contrast, radio galaxies are typically identified by their powerful radio emissions, and their host galaxies are often more readily observable.4315
- Classification: Quasars are considered extreme examples of galactic activity. Radio galaxies fall between quasars and Seyfert galaxies in terms of their level of activity.1
- Evolutionary Context: Evidence suggests that the intensity of these phenomena depends on the amount of fuel—gas and stars—falling into the central black hole. Quasars were significantly more common in the early universe, roughly 10 billion years ago, when galaxy densities were higher.1