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"Death Zone" of the Pinwheel Galaxy's Outer Rim


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 Research from the Spitzer Space Telescope has revealed that this outer red zone of the massive Pinwheel Galaxy (twice the size of the Milky Way!) lacks organic molecules present in the rest of the galaxy. NASA's Chandra X-ray Observatory image of the Pinwheel (above) is one longest exposures ever seen of a spiral galaxy in x-rays. The glowing lights indicate massive stars, black holes and supernova explosions, all wrapped in the hot gas "arms" of the galaxy.

The organics, called polycyclic aromatic hydrocarbons, are dusty, carbon-containing molecules that help in the formation of stars. On Earth, they are found anywhere combustion reactions take place, such as barbeque pits and exhaust pipes. Scientists also believe this space dust has the potential to be converted into the stuff of life.

Spitzer found that the polycyclic aromatic hydrocarbons decrease in concentration toward the outer portion of the Pinwheel galaxy, then quickly drop off and are no longer detected at its very outer rim. According to astronomers, there's a threshold at the rim where the organic material is being destroyed by harsh radiation from stars. Radiation is more damaging at the far reaches of a galaxy because the stars there have less heavy metals, and metals dampen the radiation.

The findings help researchers understand how stars can form in these harsh environments, where polycyclic aromatic hydrocarbons are lacking. Under normal circumstances, the polycyclic aromatic hydrocarbons help cool down star-forming clouds, allowing them to collapse into stars.

Regions like the rim of the Pinwheel, as well as the very early stars, form without the organic dust. Astronomers don't know precisely how this works, so the rim of the Pinwheel provides them with a laboratory for examining the process relatively close up.

The image of the Pinwheel Galaxy below combines data in the infrared, visible, ultraviolet and X-rays from four of NASA's space-based telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101's tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-ray vision, all at the same time.




The Daily Galaxy via



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