M15 is a globular cluster in Pegasus with a population of approximately 100,000 stars. Astronomers believe that M15 has experienced a phenomenon called "core collapse" where higher mass stars and binary systems migrate towards the center of the cluster. The cluster gravitationally reorganizes itself and ends up with an extremely dense core. Astronomers also believe that M15's core may contain a black hole of 500 to 3500 solar masses.

In this photo, North is up. This image is cropped to 66% of the original full frame.

Exposure Details
Lens	Celestron C-8 SCT with Celestron focal reducer
Focal Length	1160mm
Focal Ratio	f/5.8
Mount	Schaefer GEM - 7 1/2 Byers Gear
Guiding	ONAG On-Axis Guider with PHD Guiding
Camera	Canon 450D - Gary Honis modified
Exposure	74 x 180 seconds plus 26 x 60 seconds at ISO 100 - a little over 4 hours total
Calibration	30 darks, 30 flats, 30 bias
Date	October 2, 2012
Temperature	66F
SQM Reading	Brighter than 19.0 (Bortle 7 - Full Moon)
Seeing	3 of 5
Location	Pine Mountain Club, California
Software Used	Images Plus 4.5 for camera control, calibration, stacking, digital development, multiresolution sharpening, smoothing and noise reduction. Photoshop CS5 used for levels and curves, color balance, high pass filter, star shrinking, saturation adjustments, HDR combination, HDR toning, smart sharpen, match color, lab color,. Gradient Xterminator for gradient removal. Carboni Tools for additional saturation adjustments, noise reduction, and smoothing.
Notes	Because M15 has such a bright core, I took a sequence of shorter 60 second exposures. I used these shorter exposures to HDR combine with the long exposures and bring out some details in the core of the cluster. Commonly these details are overexposed in images of M15. I am pleased that this image came out as well as it did, as I opted to photograph this object at Full Moon (which is usually less than ideal).