Messier 51 - The Whirlpool Galaxy
One of the most famous galaxies in the northern sky is definitely Messier 51 in the constellation "Canes Venatici" - a beautiful "wheel of fire" at
a distance of 28 million light years.
With a diameter of 76,000 light years Messier 51 is a little smaller than our own Milky Way and is classified as a "Sc- spiral galaxy". The total
mass is estimated to be 160 billion solar masses. Right next to it lies NGC 5195, which interacts with Messier 51 and has crossed the disk of the
Whirlpool Galaxy twice, about 600 million years ago and 50 to 100 million years ago. Currently, it is slightly offset behind it.
Due to these encounters, an unusually large number of stars (starburst) are currently forming in the core region and in the spiral arms. According
to estimates, this will continue for the next 100 million years. Especially in the UV range the many star forming regions can be seen very well.
One of the brightest is located in the bridge between Messier 51 and NGC 5195. The good visibility in the UV can be explained by the fact that
many young and hot O/B stars form, which emit most of their radiation in the UV spectrum. These stars live only a few million years before they
end as supernovae. In the last 17 years alone, 3 supernovae have been observed in Messier 51, the last in 2011.
The Whirlpool galaxy is considered a type II Seyfert galaxy because of its active galactic nucleus. The supermassive black hole at the center of
Messier 51 has a mass of about one million solar masses. On images of the HST a dark structure in the shape of an "X" can be seen. The wider
part of the "X" is probably a dust torus with a diameter of 100 light years, which surrounds the black hole in the center. In recent images, a point
of light has also become visible, which is thought to represent the actual core of Messier 51. With a diameter of only 5 light-years and the
luminosity of a million suns, this could very well be the case.
But what can be seen of all this in a large telescope?
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With 12" the spiral arms can be seen - with 20" Messier 51 lives up to its name "Whirlpool galaxy". At 200x the spiral arms stand out clearly from
the black sky background and reveal some structure. If you see the galaxy under a dark sky for the first time with a 20", you will be overwhelmed
by the beauty of this galaxy. I still feel the same way, even though I have seen the galaxy many times, but it still fascinates me every time. :) :)
When I had digested the first impression, I started to examine the individual areas of the galaxy more closely. In the structured spiral arms you can
find many many HII regions, which some of you may know from photos. With 20" 11 of them were often very faint at V=270x, but clearly visible
with indirect vision. In my opinion, the brightest ones should be doable even with 16".
Of course the companion galaxy NGC 5195 is also very interesting. In the center you can find a very bright stellar core, while from the south a
dust band extends into the galaxy.
The goal was to make a detailed drawing of this beautiful pair of galaxies - I hope I succeeded.
