M81 & M82 galaxies
These galaxies are in the constellation of Ursa Major at a distance of about 7 million light years. They are physically associated. Observations at non-optical wavelengths (eg, radio) have shown swirls of gas connecting the two. They are interacting gravitationally. It appears that M81 (a normal-looking spiral, on the left here) has caused M82 (an irregular galaxy) to become very active in star formation.
Canon EOS5DMkII 254mm Newtonian @ 1200mm 101 x 10s f/4.8 ISO3200 2010-3-2 20:06:28-20:31:49 UT