Image Credit & Copyright: Don Goldman, Astrodon Imaging (http://www.astrodonimaging.com)
Sharpless 308 (also known as Sh2-308, S 308 or RCW 11) is a cosmic bubble of nearly 60 light-years across, located some 5,200 light-years from Earth in the constellation of Canis Major, the Greater Dog. Known as a Wolf-Rayet bubble, it has an age of about 70,000 years and an expansion velocity of about 60 kilometers per second.
Wolf-Rayet (WR) stars are extremely rare and short-lived super-hot stars which start their lives with dozens of times the mass of our Sun, but rapidly loose most of it through a powerful stellar wind, with speeds up to 2000 km/s. They are also highly luminous, from tens of thousands to several million times the luminosity of the Sun, although not exceptionally bright visually since most of their output is in far ultraviolet and, in the case of Sharpless 308, even in X-rays (it is one of only two known Wolf-Rayet bubbles that emits X-rays). Often occurring in binary systems, WR stars are candidates for being progenitors of long-duration Gamma Ray Bursts.
This bubble is blown by the fierce winds of the huge Wolf-Rayet star HD 50896 (also known as WR 6 or EZ Canis Majoris) – the blue star near the centre of the image. And, like any good bubble, Sharpless 308 will eventually burst. It will disperse its stellar material into the surrounding space within a few million years, to explode as a supernova.
Sharpless 308 has been said to resemble a dog, with a protruding “ear” (upper left), and a “snout” below a pair of piercing “eyes” that includes the blue WR star and its yellow counterpart (Omicron 1 CM).
This image was taken with Astrodon 3 nm OIII and 5 nm H-a filters. Star colors were taken with Astrodon Generation 2 RGB filters and blended in. Narrowband colors are mapped to Red = H-a, Green = Blue = OIII. North is toward the left.