Getting To Know The Whirlpool Galaxy
Take a close look in the constellation, Canes Venatici, which lies below the Big Dipper, and if you look below the last star of the handle of the dipper you will find Messier object, M51, or the Whirlpool galaxy. The galaxy also has the New General Catalog classification, NGC 5194. A quick look at the enhanced image from the Hubble Space Telescope below, easily demonstrates why it is known as the Whirlpool galaxy. Also evident is its companion, NGC 5195, which is intimately connected to M51.
This Hubble image clearly shows the dark dust lanes that lace the arms of the galaxy. The blue color in the arms is due to the hot, blue stars (type O and B stars) that have formed in these dust-rich regions of the galaxy. The pinkish knots are star forming regions – stellar nurseries. These are creating stars that will shine on long after the short-lived blue stars that populate the arms have consumed the last of their fuel.
The image also clearly shows the connection between M51 and its companion, NGC 5195, as it pulls on the arm of M51. For many years it was unknown if it was interacting with M51 or just in the line of sight behind M51. It wasn’t until observations from radio telescopes revealed that they are interacting with each other, and this interaction may have generated the density waves that contributed to the spiral structure of the Whirlpool galaxy.
This composite image above of visual and radio wavelengths from the National Radio Astronomy Observatory, using the Very Large Array (VLA), shows the structure of the interacting pair of galaxies. The blue sweeping curves and envelope that surrounds the galaxy is from neutral hydrogen atoms, and indicates that these two galaxies have been gravitationally entwined for a long time.