Omega Centauri, NGC 5139

Arguably the finest globular cluster in the sky, omega Centauri is a glittering collection of an estimated 5 million stars occupying a region of space about 150 light years across and 16,000 light years away. 

Even a cursory examination of the image below reveals that the cluster contains (old) yellow stars and (young) blue stars, an observation which is contrary to the general understanding that stars in globular clusters formed at the same time. That the stars in omega Centauri have a range of ages and metallicities implies that star formation has continued throughout the 12 billion year age of the cluster and it has evolved in a different way to other such objects. An explanation that satisfies these properties is that omega Centauri is the remnant core of a satellite galaxy that has had its outer regions assimilated by the Milky Way leaving just the core behind. Measurements of star motions near the core have been interpreted to suggest that an  approx 1x104 solar mass blackhole resides there.  

 

Camera: SBIG STL11000M, Astrodon filters Scope: Takahashi TOA-130, f=1000mm, f7.7 with field flattener, (cropped fov ~1.5 x 1.0)
Mount: Takahashi EM-200 Temma 2 Guiding: external, e-finder
Filters/Exposures: R:G:B = 20:20:201h Location: ASV's Leon Mow Dark Sky Site, Heathcote, Victoria, Australia
Date: March 2015 Processing: CCDStack2, RegiStar and Photoshop CS5