M13 - Hercules Globular Cluster
Globular Clusters are still mysterious objects and not well understood by astronomers.   They orbit the outskirts of galaxies such as our own Milky Way Galaxy.  Globular clusters are almost always comprised of older Population II stars and have lower metal content since less metal was available in the younger universe when they were formed.  By contrast, our sun is a younger, metal rich Population I star.   The density of globular clusters is relatively large and upwards of a million times more dense than our own area of the galaxiy.   But even at this density, the average distance between stars at the center is greater than ten times the distance from our sun to pluto.   What causes these stars to organize in this way is still not understood well.   It is possible that massive black holes rule the center of these objects but until recently it was only a theory.   Over the past couple years researches have found black holes at centers of several globulars, which now makes them seem more like small galaxies and the line is bluring between globlars and the smallest galaxies called dwarf galaxies.    In this image you can see that many of the stars are old and red in color with a splattering of hotter, younger blue stars.  Off to the right in this image is a very distant spiral galaxy, IC 4617.   M13 orbits the center of the Milky Way Galaxy about 25,000 light years from earth and out of the plane of the disc of our galaxy.  It contains as many as 300,000 stars.  For comparison, the largest globular clusters contain over 1 million stars.
Optics: RC Optical System 20" F/8.2 (4165.6 mm Focal Length) Date: May 2014
Camera: SBIG STXL-11000 with Adaptive Optics Location: Columbus, Texas
Exposure: LRGB = 50:15:15:15 minutes Imager: Kent E. Biggs