Cygnus A - Radio Galaxy
"Cygnus A" is (of course) located in the constellation "Cygnus" and is the second most powerful radio source in the sky. It was discovered in 1939,
but only in 1951 one could assign an optical counterpart to this source. It was a galaxy with a redshift of z=0.056, which corresponds to a distance of 760
million light years. This makes "Cygnus A" the strongest extragalactic radio source.
The radio galaxy is classified as "cD" (which means "central dominant") - furthermore it is a so called giant ellipse with a diameter of 400.000 lightyears.
It is assumed to be about a 1000 times as massive as our home galaxy. Moreover, it is located in the center of a rich galaxy cluster with 200 members,
which, however, is hidden behind the dust of the Milky Way. In the core of "Cygnus A" there is a black hole with a mass of nearly 3 billion solar masses,
which is surrounded by a huge dust torus. This black hole is responsible for two jets leaving the galaxy in opposite directions. They hit the intergalactic
medium surrounding the galaxy at great distances from it. The gas masses in these areas are strongly heated by the energetic particles of the jets and thereby
emit the observed radio waves. So it is not the host galaxy itself that is the origin of the radio emission, but the two nearly symmetric gas clouds.
This makes "Cygnus A" an absolutely exciting object, at least from the astrophysical point of view.
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The question is of course, what of all this can be seen in a 20" telescope. To be honest - not very much. Because "Cygnus A" is located in a relatively dense
area of the summer Milky Way, it needs little patience to get by starhopping to the galaxy, which is located almost centrally between two 13mag and 14mag
bright stars. As expected, at first nothing at all was visible at a low magnification.
When I then went to 380x, I could perceive an extremely faint and rather small diffuse spot at the galaxy's position, which popped out of the pitch black sky
background every now and then. I also thought I could see a very faint star in the center of the galaxy. This could even be the active galaxy nucleus. The halo
of the galaxy is really tiny with a visual diameter of only 10" (arcseconds) and does not nearly reflect the true dimensions of the galaxy.
The two blue lobes are of course not visible in the telescope, but have been added to the drawing for illustrative purposes only.
Although "Cygnus A" is not an easy object visually, it is on my observing list every summer. Simply because the physics behind it is extremely compelling.
