Image of the Day: The Elusive Beauty of Radio Galaxies


As radio astronomers mapped the sky, they found several bright radio sources associated with distant galaxies. One of the brightest was the radio source Cygnus A (above). Cygnus A is a double-lobed radio source. Also notice the jets from the center. At the center sits a giant elliptical galaxy, at a distance of ~ 200 Mpc. At this distance, the lobes are separated by more than 100 kpc, and they have a radio luminosity of 1045 erg/s, 106 times greater than the radio luminosity of normal galaxies.

Radio galaxies, unlike Seyferts, are generally hosted by elliptical galaxies, not spirals. Seyferts are also radio quiet. M87, the central elliptical in Virgo below, also is a radio galaxy. It is close enough that we can examine its center in detail, where we can actually see the jet in the optical.


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