It's uncommon for us land based photographers to image a pair of interacting galaxies, especially when they're 28 million light-years away.  This galaxy pair are located in the constellation Canes Venatici and can be found just southwest of the last star in the tail of the big dipper. 

This image was taken through a 120mm apeture; 840mm fl; f/8 SW Esprit telescope.  Spiral bands are apparent in this image, with HII regions visible. M51 can be seen to be attached to M51b (a dwarf galaxy).  In dark sky regions it's viewable with a good set of binoculars - as a faint smudge of course. 

Interacting is a nice term for colliding and merging.  It's something galaxies do quite frequently.  Hubble has shown us that with upwards of 800 billion galaxies in the universe it's to be expected.  The pronounced spiral structure of the Whirlpool Galaxy is believed to be the result of the close interaction between it and its companion galaxy NGC 5195 (M51b), which may have passed through the main disk of M51 about 500 to 600 million years ago. In this proposed scenario, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 million years ago until it is where we observe it to be now, slightly behind M51.

The Whirlpool Galaxy lies 28 million light-years from Earth and has an estimated diameter of 76,000 light-years. Overall the galaxy is about 43% the size of the Milky Way. Its mass is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy.

A black hole exists at the heart of the spiral. A pair of ionization cones extend from the active galactic nucleus.

Gear used: SW Esprit 120ED scope: ASI2600MC camera: SW EQ6r Pro mount; ZWO OAG; ASI290mm mini guide camera; sesto senso 2 electronic focuser; QHY polemaster; pegasus pba; I3 NUC

Software used: Image acquisition via Astrophotography Tool (APT); guiding via PHD2; Image calibration, registration, integration and processing in PixInsight