Planewave CDK 12.5in; AP 1100GTO AE
QHY600M, - Antlia Broadband and 3.5nm Ha Filters
L: (43 x 180s, Bin 1, Gain 100)
H: (26 x 720s Bin 1, Gain 100)
R,G,B: (22,29,30 x 210s, Bin 1, Gain 100)
Total integration time = 12.1 hrs (Apr 22-24, 2025) Maple Bay, BC, Canada

M100, is a huge grand design spiral galaxy lying in Coma Berenices and is part of the massive Virgo cluster. It's visible diameter (in the image) is 165,000 ly (roughtly twice the visible diameter of the Milky Way, but its true diameter is likely many multiples of this when you consider the invisible extensions of the monatomic and diatomic hydrogen arms.
Unlike the Milky way, which is a barred spiral (having a "bar" or stars and material at its centre), M100 is a considered an "intermediate" galaxy - much like Caldwell 5 shown in a previous image. In this context intermediate means, if it has a bar it is either too small to see or is in the process of forming.
M100 is also considered a starburst galaxy, due to the high rate of star formation taking place. In particular, there is a lot of star formation taking place right at its core, as evidenced by the strong Halpha signal bands near the centre of the visible spiral. Halpha emissions occur in hydrogen atoms recovering from UV bombardment from new stars and represent one of the few conditions that allow us to see gaseous hydrogen directly. The emissions create the red blotches we in our visible light galactic images.
Most images of galaxies are much brighter near their core than M100, with this Ha signal being overwhelmed by the stars that are created there. It should be noted, that the spiral arms near the core are at a much finer scale than further out and this results in trend of smaller, but longer lived stars here. Nonetheless, there are lots of Halpha indications that stars are also being created further out in the arms as well.
To understand the circulation of hydrogen with a spiral galaxy, I am posting an analysis of M100 on my web page at aprealspace.com. On this posting, I will be discussing how hydrogen, both in its monatomic and diatomic forms, moves around the galaxy.