Current Knowledge
It is believed that the galaxies NGC 5194 and NGC 5195 are interacting with each other, and that these interactions have caused many abnormalities such as assymetric arms, intense star forming regions caused by the granitational impulse on the gas clouds of the galaxies, and other effects typical of interacting galaxies.
Simulations illustrating the interaction between NGC 5194 and NGC 5195 have shown that it is believed that NGC 5194's spiral structure was the result of NGC 5195 passing through the main disk of NGC 5194 about 500 - 600 million years about. It is believed that it crossed the disk once again 50 - 100 million years ago causing NGC 5195 to be slightly behind NGC 5194 (from our view), which is where it is believed to still be today.
It is believed that in the heart of the spiral lies a black hole surrounded by a ring of dust. The dust ring is almost perpendiular to the fairly flat spiral galaxy, and at a completely different axis a secondary ring actually crosses the primary ring. This event is uncommon and it causes a pair of ionications cones to extend from the axis of the primary dust ring. This phenomenon has drawn many astronomers interested in studying black holes.
The picture above shows the nucleus of M51, and the prominent X formation which is caused by the intersecting dust rings.