Distance: 31 Million Light Years
Magnitude: 8.4 M51a
Magnitude: 10.5 M51b
Size: 11 x 7 Arc Minutes M51a
Size: 5 x 5 Arc Minutes M51b
Galaxy Type: M51a Spiral Sc
Galaxy Type: M51b Dwarf
Camera: QSI 683
Mount: AP 900
Exposure: L 11×300 Bin 1, RGB 11×150 Bin 2
Messier 51 is a spiral galaxy located in the constellation Canes Venatici. The spiral arms show well in short exposures and are active star forming regions containing thousands of nebulous areas along with hundreds of young star clusters. A 2011 research paper from Seoul National University has found about 19,600 HII regions in this galaxy. This beats any prior attempts to catalog these areas because the earlier attempts were based on ground observations that limit the resolution (1.8” per pixel) and ability to resolve these small objects. The new counts are based on images from the Hubble Space Telescope which has a resolution of .05” per pixel with a point source FWHM of .1”and can define these areas much better. The image used for the study covered a 7.2’ x 10.2’ area of sky. To put the resolving power of Hubble in perspective, if you could see as well as Hubble and you were in New York City you could see two fire flies one meter apart in San Francisco!
M51 is actually two galaxies that are gravitationally bound with M51a being the large spiral galaxy and M51b as the smaller fuzzier one.
M51a is an active star forming galaxy partly due to its interaction with M51b. Observations show that when M51b passed through M51a it excited the region and accelerated star formation. M51b has moved through M51a from front to rear and will move from rear to front in the future. The theory is that this cycle will continue until both galaxies become one. At question is the timing between these passings but one model suggests 100 million years, another 300 million years, and another at 500 million years. Many new star clusters containing Type O and B stars are located in the spiral arms of M51a and this gives the arms their bluish color. Many reddish nebulous regions are also contained in the arms and this is the fuel for future star generation. The central core of the galaxy contains many of the older stars in the galaxy as indicated by their reddish yellow color. Also noticeable are many dust lanes in the arms.
M51b is classified as a dwarf galaxy (Wiki) even though it is 20,000 light years across (NASA). A 2011 research paper by Seoul National University calls M51b a barred lenticular SB0 galaxy. A 2006 research paper from Seoul National University found that M51b contains a rare type of globular cluster called faint fuzzy star clusters. These faint fuzzy star clusters are much larger than typical Galactic globular clusters and also much redder but are relatively young at 1 billion years. What the authors of this paper also noticed was that their location in the galaxy roughly matched the northern spiral arm of M51a indicating gravitational interaction induced their creation.
As a side note, this is the first galaxy image with my new 10” RC. I kept the exposure times short because of high clouds and humidity. Typical spring weather here!
[SEDS, Wiki, Seoul National University 2006 + 2011, Hubble Site.org]