Seyfert galaxies are a type of active galactic nucleus characterized by strong emission lines, high luminosity, and a compact central region. The first Seyfert galaxy was discovered in 1943 by Carl Seyfert, who identified it as a class of “emission-line nebulae”. These objects are now known to be powered by supermassive black holes at the centers of galaxies.
Seyfert galaxies are some of the most luminous objects in the universe. They have been observed across the electromagnetic spectrum from radio waves to gamma rays. The high luminosity is thought to be due to accretion onto the central black hole. In some cases, this accretion can be so efficient that the resulting radiation can outshine the rest of the galaxy!
The emission lines seen in Seyfert galaxies are produced when gas falls into the central black hole. As this gas heats up and emits light, we see bright lines in specific wavelengths corresponding to different elements. For example, hydrogen will produce a bright line at wavelength 656 nanometers (red), while oxygen will produce a line at 500 nanometers (green).
The small size of the central region is another key feature of Seyfert galaxies. In many cases, we can resolve individual stars near the center of these galaxies using telescopes like Hubble. This provides strong evidence that there is indeed a supermassive black hole at the center!
Seyfert galaxies are important for our understanding of how active galactic nuclei work. By studying these objects, we can learn about how matter behaves near extreme gravitational forces, and how energy is generated and released on cosmological scales.