Messier 101 - Pinwheel Galaxy
In the constellation "Big Dipper", at a distance of about 22 million light-years, there is a large spiral galaxy called Messier 101, or "Pinwheel- Galaxy." With a
true diameter of 170,000 light-years, it is 1.5 times larger than our own Milky Way and is estimated to contain over 1 trillion stars. It was discovered in 1781
by Pierre Méchain, while the spiral structure was first seen by Lord Rosse in the mid-19th century.
Messier 101 has an apparent magnitude of 7.9mag, but the light is spread over a huge area of 28.8'x26.9' (arcminutes), which is almost the apparent size of
the full moon. Accordingly the surface brightness is very low with a value of 14.6mag/'˛.
The absolute magnitude is M= -21.6mag, which is equivalent to a luminosity of 47 billion suns. The total mass of Messier 101 is given with 100 billion solar
masses, the mass of the bulge with 3 billion suns. Due to interaction with companion galaxies, the spiral arms are slightly disturbed and bent outward. In addition,
star formation has been fueled in M101, which is why there are nearly 1,300 HII regions in this galaxy. Some of these regions are so bright that they even got a
number in the NGC catalog. The galaxy is surrounded by a halo of 150 globular clusters.
In the center no supermassive black hole has been detected yet, because no X-ray emission has been registered which would indicate a SMBH.
So far 5 supernovae were observed in Messier 101, the brightest one reached a maximum brightness of 9.9mag in 2011. The last supernova appeared in 2023
with a magnitude of 11.0mag and was of type II. Its designation was "SN 2023ixf".
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Messier 101 is in my opinion one of the most interesting and beautiful galaxies in the northern firmament, but only if the sky is really dark. Because with strong
light pollution not much of this beauty can be recognized and Messier 101 degenerates to an unsightly diffuse spot... By the way, it shares this fate with Messier
33 and Messier 74.
But this spring the sky was wonderfully clear at nearly 1,000m a.s.l, so I was finally able to capture the "Pinwheel Galaxy" in its entire beauty with my 20" f/3.
The spiral arms were clearly visible and even slightly structured this night, the central region quite bright with a nearly stellar core. A closer look also revealed
many HII regions.
When I increased the magnification to 270x I was able to see almost point-like objects in the HII regions (marked with arrows). They are estimated to be SSCs
(Super Star Clusters). So you observe a DeepSky object in a DeepSky object in a DeepSky object. So DeepSky to the power of 3 or something like that.... Great
story anyway!
