Messier 100 - Spiral Galaxy
Messier 100 is a "grand design" spiral galaxy. Only about 10% of all spiral galaxies belong to this group - they are characterized by particularly prominent
and well-defined spiral arms. The "SAB"- type galaxy was discovered in March 1781 by Pierre Méchain in the constellation "Coma Berenices". It has an
apparent magnitude of 9.3mag and a size of 7.4'x6.3' (arcminutes) and is best observed in the spring months.
The true diameter of Messier 100 is determined to be 107,000 light years. The absolute magnitude can be calculated from the known distance of 55 million
light years to M= -21.8mag, which corresponds to a luminosity of 45 billion suns. The galaxy is also described as "starburst galaxy", because within a small
ring near the center many new stars were born in several phases in the last 500 million years.
According to a 2018 paper, a supermassive black hole (SMBH) with a mass of 25+-2 million solar masses has been detected in the core of Messier 100.
Due to the fact that we are looking almost directly at the galaxy from above, 7 supernovae have been observed in the last 100 years, the two brightest in the
new millennium being "SN 2006X" with a maximum brightness of 15.3mag and "SN 2019ehk" with 15.8mag.
Messier 100 has two companion galaxies (NGC 4323/28), the former is connected to M100 by a very faint light bridge.
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When pointing a 20" telescope at Messier 100 for the first time, you may be a little disappointed. This is because despite the relatively high overall brightness,
the galaxy appears quite faint. This is due to its low surface brightness. So to see the beautiful spiral arms you need a very dark sky. If everything suits and you
hide under a dark cloth for a few minutes, the spiral arms peel out of the galaxy halo.
Unlike Messier 51, the arms don't immediately pop into your eye, it's all a bit more gentle and subtle. This is also what I like about this galaxy. You have to take
a little time to see how the faint arms wrap around the nucleus. You can also see some brighter spots. The core area appears slightly mottled, although I could
not pin down the structures.
Under a very dark sky with a large aperture, Messier 100 is a wonderful sight that is hard to tear yourself away from.
