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Twin Jets from Radio Galaxy Star Cygnus A
Cygnus A is the most powerful radio galaxy in our corner of the Universe. At a redshift z = 0.0565 (distance of about 700 million light-years), its nature remains mysterious. The first photographs of Cygnus A showed two clumps of luminous material, which led Walter Baade and Rudolph Minkowski to speculate that the radio emission was somehow linked to a galaxy collision. Others saw a poorly resolved version of Centaurus A, bisected by a thick dust lane. The HST image shown at the right reveals much detail, but doesn't quite clear the matter up. We see dust and an odd Z-shaped pattern. Much of this light in some regions comes not from stars, but from gas ionized by the nucleus. This is a narrow-line radio galaxy, but infrared and polarization measurements show that from some directions it would appear as a broad-line object and perhaps as a quasar, so that there is plenty of radiation in some directions to light up the gas.
Cygnus A is an excellent example of the Fanaroff-Riley (FR) type II radio sources, characterized by faint, very narrow jets, distinct lobes, and clear hot spots at the outer edges of the lobes, often where the jets intersect the outer edges. These are in general more powerful radio sources than the FR I objects, with the difference being frequently attributed to faster motion (95% the speed of light) of the jet material in the stronger FR II sources.
The jets are generated by a supermassive black hole at the galaxy's core—a black hole with 2.5 billion Solar masses. Compare these jets with the jet from galaxy M87, which harbors a black hole of similar mass.
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