M 51 - Whirlpool Galaxy
NGC 5194 and 5195 form a striking pair of interacting galaxies. Charles Messier discovered M 51 (NGC 5194) in the year 1773. The fainter core of NGC 5195 was first observed by Pierre Mechain in 1781. Lord Rosse became aware of the spiral structure in 1845 - it was the first time that this structure was observed long before the real physical nature of these objects was known.
The last close encounter of both galaxies took place about 400 million years ago. It induces massive star creation in the larger companion. For this reason the spiral arms of M 51 are very bright. NCG 5194 is possibly a barred dwarf spiral galaxy loosing most of its interstellar matter during the encounters. Therefore, no star creation was observed in the dwarf galaxy. Additionally, NGC 5194 looses many of its old stars. They form weak tails that can be seen in the images. Some of these stars will become part of the larger spiral galaxy, others will be scattered into the intergalatic space.
NGC5195 is located about 500,000 light years behind NGC 5194. M 51 is about 27 million light years away. Many of the faint objects in the image are remote galaxies. Some of them are about 3.5 to 4 billion light years away.