PH 207 topics
The above is an x-ray image of the central region of the radio galaxy, Centaurus A. Radio galaxies actually show very short peak wavelengths, but their radio emissions allow us to probe the structures like the immense lobes seen in Cygnus A, at the top of the page. The light signatures from radio galaxies are much more extended than the Seyfert galaxies. The high energy x-ray light from the nucleus encounters gas as it expels from the center of the galaxy, being repeatedly absorbed and re-emitted. This absorption and re-emission tends to lower the energy of the photons, producing the extended lower wavelength radio light we see in the lobes. Some radio galaxies appear more core-dominated, but it is likely that the galaxy happens to be positioned such that we are looking inward along the radio lobe. Some galaxies are rotated just right to have their jets pointed straight at us, so that the light is extremely intense. We call them blazars, since they are so bright.