This is M51, the Whirlpool Galaxy, which I last shot 4 years ago. It’s fairly small, so it’s difficult to get a sharp image, and I don’t often try. The above version is cropped to less than half the full frame, and the galaxy is still a small portion of the area. Below is the (almost) whole image:
It looks a bit sharper this way, and you get to see at least one more galaxy in the lower left corner.
This image was put together from about 2 hours of luminence data and 2 hours of RGB data. As with the previous post (Whale Galaxy image), I used all or most of the luminence data for the background and fainter nebulosity, but only the best/sharpest frames for the brighter parts (most stars and maybe half of the galaxy area). This technique makes only a subtle difference, but it helps because the dark regions tend to have less detail and more noise, and we pay more attention to the sharp details in the bright regions. The same differentiation is sometimes used to selectively apply noise and sharpening filters for shadow and highlight regions, respectively.
M51 is roughly 23 million light-years from Earth, and is found in the constellation Canes Venatici. It is really 2 separate galaxies (M51a on the left and M51b on the right) that are interacting.