Today we know that Messier 51, also catalogued with the designation NGC 5194 (M51a), is a grand-design spiral galaxy located approximately 23 million light-years away from our planet. It is interacting gravitationally with its smaller companion galaxy, NGC 5195 (M51b). This interaction is responsible for the pronounced and beautifully defined spiral arms that make M51 such a popular imaging target.

With an apparent magnitude of about 8.4, Messier 51 is good target even for small telescopes under dark skies. Visually observer may see its bright core and hints of spiral structure. It might have been the bortle 6 skies I have lived under back in the day, but I personally never seen it with my own eyes while using my old Omegon Advanced 150/750 telescope. But by using a deep-sky camera, M51 was finally obtainable for me. Even using my smaller William Optics Redcat 51 telescope, I was able to capture the dark dust lanes in the whirpool of M51a and even some details in M51b.

The Whirlpool Galaxy spans roughly 60,000 light-years in diameter, it is smaller than both our Milky Way and the Andromeda Galaxy, yet its structure is really well defined. The tidal forces between M51a and M51b have triggered waves of star formation, illuminating its spiral arms with clusters of young, hot blue stars and red emission nebulae. In the future I would like to go back to the object and use my new Optolong L-eXtreme filter to capture these red emission nebulae.

With extensive integration time, such as my final image with 53 hours of data, even fainter structures begin to appear that are not part of M51, but are surrounding our own galaxy, known as the Integrated Flux Nebula (IFN). The IFN is extremely faint interstellar dust illuminated by the combined starlight of the Milky Way. The Integrated Flux Nebula is something I have captured before. The first time was in 2024 when I was phographing Messier 81, the Bode’s Galaxy and its friend Messier 82, the Cigar Galaxy. After 8 hours of integration, a faint glow of the Integrated Flux Nebula became visible. After 18 hours, the IFN had developed so much detail that it almost became the main feature of the image itself. It remains one of my favorite images, and now that I have gained considerably more experience in processing astrophotography data, it may be time to revisit and reprocess it.

Like I just explained, this interstellar dust is not part of M51 itself, but that does not mean the Whirlpool Galaxy does not have something spectacular of its own. I call them the “teeth” of the Whirlpool Galaxy. Enormous faint tidal streams extending far beyond both M51a and M51b, formed by their ongoing gravitational interaction. These elongated, teeth-like streams of stars are remnants of M51a and M51b their interactions over million of years. On the left side of M51b in my image, the massive tidal stream extends even farther, although it remains extremely faint even after 53 hours of integration time. Before I started this project, I did not even know that the IFN and this extended tidal stream were present in thi field of view, so it was a very nice surprise to find them in my final stack.

Something else that I really like about this final image are all the tiny orange dots you see. Some of them are stars in our Milky Way, but the small less star-shapes spots are actually background galaxies that are really far away. Some of them even a few billion light-years! Compared to M51, that lies at a distance of 23 million light-years from us, being able to see those spots feels insane.