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This richly detailed new view from the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile shows the star-forming region Gum 15. This little-known object is located in the constellation of Vela (The Sails), some 3000 light-years from Earth. The glowing cloud is a stunning example of an HII region. It also has a similarity to a more famous HII region, the Trifid Nebula (M20). Hydrogen (H) is the most common element in the Universe, and can be found in virtually every environment investigated by astronomers. HII regions are different because they contain substantial amounts of ionised hydrogen - hydrogen atoms that have been stripped of their electrons through high energy interactions with ultraviolet photons - particles of light. As the ionised hydrogen nuclei recapture electrons they release light at different characteristic wavelengths. It is one of these that gives nebulae such as Gum 15 their reddish glow - a glow which astronomers call hydrogen alpha (Hα). In HII regions the ionising photons come from the young hot stars within the region, and Gum 15 is no exception. At the center of this image you can see one of the culprits: the star HD 74804, the brightest member of a cluster of stars known as Collinder 197. An HII region like this one might give birth to thousands of stars over a period of several million years. Some of these stars cause it to glow and sculpt its shape, and it is these stars that will eventually destroy it. Once the newly minted stars have passed through their infant stages, strong winds of particles will stream away from these large stars, sculpting and dispersing the gases around them, and when the most massive of these stars begin to die, Gum 15 will die with them. Some stars are so large that they will go out with a bang, exploding as supernovae and dispersing the regions last traces of HII, leaving behind just a cluster of infant stars.
Image Credit: ESO
Image enhancement: Jean-Baptiste Faure