NGC 6946 - Fireworks Galaxy
The "Fireworks Galaxy" is located at a distance of ~24 million light years in the constellation "Cepheus" and is therefore close to the galactic plane.
Unfortunately, this has the consequence that the light of this beautiful galaxy is weakened by some dust in front of it and thus appears much fainter
than it would without dust. Initially, NGC 6946 was thought to belong to the local group, but it is too far away from us for that. It is now counted
as a member of the Virgo Cluster.
With a diameter of about 40,000 light-years, NGC 6946 is only one-third the size of our Milky Way and has about half the stars. It is listed as an
intermediate spiral galaxy. It has some exciting peculiarities, such as nearly starless patches in the spiral arms, a "red ellipse" (which is thought to
be a very large supernova remnant) and also some dark lines in the arms can be found.
Unlike many other spiral galaxies, no indications of a supermassive black hole have yet emerged in NGC 6946, suggesting that the mass of the
SMBH at the center of a galaxy is not necessarily correlated with the mass of the bulge.
In the last 100 years, 10 supernovae have flared in NGC 6946, putting the galaxy at the top of the supernova frequency statistics. Especially bright
was "SN 2004et" with a maximum brightness of 12.5mag, that could be seen even with 8" aperture.
Another star deserves special mention: its name is "N6946-BH1" and the star is believed to be a so-called "prevented supernova". Until this event in 2009 it
was assumed that a black hole can only form after a supernova explosion. But in this particular case it seems that the nucleus collapsed directly into
a black hole. The increase in brightness (which was way too small for a supernova) is explained by the fact that a neutrino burst fueled a shock wave,
which drove the stellar envelope outward.
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The observation with a 20" telescope under a dark sky reveals many structures and interesting insights - if the sky is dark enough. Because the surface
brightness of the galaxy is very low, NGC 6946 disappears in the background when the sky is brighter and almost nothing can be seen except for the
bright core area.
I found the galaxy most beautiful at a magnification of about 200x. With a little bit of patience you can see the pale spiral arms, which wind outwards
to varying distances but are only visible with averted vision. With a closer look, even brighter spots in the arms can be seen. Increasing magnification
to 270x reveals four HII regions.
#1: appears bright, large, homogeneous + roundish and is easy to detect with averted vision.
#2: on the other hand was quite difficult, because small and faint.
#3: easy to see, although not very bright.
#4: easy to see because this HII region is small and bright. It reminds a bit of NGC 604 in Messier 33 because of its location.
