M51, also known as the Whirlpool Galaxy, is another of the best known deep sky objects in the northern hemisphere. It’s one of the best places in the sky to see gravity in action. The tidal stretching of the two galaxies is readily apparent. It’s almost as if we have a still of two dancers caught just before they come together.

Of course, if two dancers come together they bounce. But, few, if any stars will collide though the gas in the galaxies can collide. The result, whenever the interaction completes will leave the two galaxies radically changed, perhaps merged into one larger galaxy. It will be a dance that our descendants can watch for millions of years as the two galaxies complete their slow motion ballet.

On a less poetic note, this image was taken at SRO on the Planewave CDK14 on which I’m an imaging team member. This is 21 hours, 20 minutes of data collected from late June to mid-July 2021. M51 was starting the night too low to collect much more data this season but that still left us with enough data to make a spectacular image!

For all the technical details, see the astrobin link.

Here is an inverted version of the image. This make it more clear that the arcs of stars below each galaxy actually connect making this interacting system much larger than it might appear at first glance.