This amazing object, nicknamed the Pinwheel Galaxy, is a large grand design spiral galaxy located 25 million light years away in the constellation of Ursa Major at a declination of +54 degrees. It is a magnitude 7.9 galaxy. The disk looks face-on to us but actually is inclined about 20 degrees. The disk is 170,000 light-years in diameter and is estimated to have at least one trillion stars.
The asymmetry of the galaxy could be due to interaction with one or more of its 6 companion galaxies, and/or a collision with another galaxy in the past. The only companion galaxy seen in this image is NGC 5477, at the left edge of the image.
M101 contains a number of clear examples of
Vorontsov-Velyaminov rows. These are straight segments of otherwise curved galaxy arms, connected by a constant angle. Straight segments are hard to explain using gravitational theory. These rows are believed to be caused by large-scale density waves although I don't understand the exact mechanism.
Note that on the Astrobin mouseover (seen by clicking on the image first and THEN mousing over), there are 10 NGC-identified objects seen within this galaxy, which I believe are the most for any galaxy. The fascinating bright blue region halfway between the center of the image and the left edge is NGC 5471, one of the largest known GEHRs - Giant Extragalactic H II Regions).
My favorite parts of this image are the Ha regions and blue star clusters seen throughout the entire galaxy, the subtle yellow glow of the central galaxy core, the large number of branching galaxy arms (I count 10), and the faint distant galaxies which can be seen through the empty space between these arms.
This is a LRGB image supplemented with Ha data.
Comments