Seyfert Galaxy

Seyfert galaxies are named after Carl K. Seyfert, who first described them in 1943. He found a whole group of galaxies with bright central regions and a strange pattern of radiation.

In a traditional galaxy, the much of the radiation comes from the galaxy’s spiral arms, where much of the star formation is taking place. But in Seyfert galaxies, there’s starlike radiation, but it’s coming from the core of the galaxy. What could be causing this was a mystery that puzzled astronomers, but we now the answer. They contain an actively feeding supermassive black hole at their core.

These monster black holes can contain millions of times the mass of the Sun, and have vast accretion disks surrounding them. It’s this accretion disk, heated to millions of degrees Kelvin that gives off the powerful radiation. An active galactic nucleus can blaze with more radiation than the rest of the galaxy. The black hole can spin at relativistic speeds, churning up the accretion disk with a powerful magnetic field. Twin jets of material are blasted out of the nucleus above and below the galaxy at near light speed. These jets can extend for hundreds of thousands of light-years into space.

Astronomers have discovered a range of galaxies with active galactic nuclei: quasars, blazars and Seyfert galaxies. They now think all of these objects are actually the same, we’re just seeing them from different perspectives, with different amounts of material falling into the supermassive black hole.

Actively feeding supermassive black holes are surrounded by a torus of gas and dust. In the case of a Seyfert galaxy, astronomers believe that we’re seeing the galaxy edge on, so the active galactic nucleus is shrouded by this torus of gas from our perspective. With a quasar, we’re seeing the galaxy at an angle, and can see over the shrouding torus to see the active galactic nucleus. And in the case of blazar, the jet of material is pointed directly at the Earth.

Seyfert galaxies are bright in the radio, infrared, ultraviolet and X-ray parts of the spectrum, but they’re invisible in the visible wavelengths of light. That’s because the visible light is being blocked by that torus of gas and dust.

We have written many articles about galaxies for Universe Today. Here’s an article about how Seyfert galaxies can consume their neighbors.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Source: SEDS.org