WASHINGTON, July 21 (Xinhua) -- Using Spitzer telescope of National Aeronautics and Space Administration (NASA), a team of U.S. astronomers have identified a zone without organics around Pinwheel galaxy, NASA reported Monday.
The fluffy-looking Pinwheel galaxy, officially named Messier 101, is dominated by a mishmash of spiral arms, according to new images taken by Spitzer, in which infrared light is color coded and the galaxy shows a swirling blue center and a unique, coral-red outer ring.
A new paper appearing in the latest issue of Astrophysical Journal explains why this outer ring stands out. According to the authors, the red color highlights a zone where organic molecules called polycyclic aromatic hydrocarbons, which are present throughout most of the galaxy, suddenly disappear.
Polycyclic aromatic hydrocarbons are dusty, carbon-containing molecules found in star nurseries, and on Earth anywhere combustion reactions take place. Scientists believe this space dust has the potential to be converted into the stuff of life.
"If you were going to look for life in Messier 101, you would not want to look at its edges," said Karl Gordon from Space Telescope Science Institute. "The organics can't survive in these regions, most likely because of high amounts of harsh radiation."
The Pinwheel galaxy is located about 27 million light years away in the constellation Ursa Major. It has one of the highest known gradients of metals of all nearby galaxies in our universe. In other words, its concentrations of metals are highest at its center, and decline rapidly with distance from the center. This is because stars, which produce metals, are squeezed more tightly into the galaxy's central quarters.
Gordon and his team used Spitzer to learn about the galaxy's gradient of polycyclic aromatic hydrocarbons. The astronomers found that, like the metals, the polycyclic aromatic hydrocarbons decrease in concentration toward the outer portion of the galaxy. But, unlike the metals, these organic molecules quickly drop off and are no longer detected at the very outer rim.
The findings also provide a better understanding of the conditions under which the very first stars and galaxies arose. In the early universe, there were not a lot of metals or polycyclic aromatic hydrocarbons around. The outskirt of the Pinwheel galaxy therefore serves as a close-up example of what the environment might look like in a distant galaxy.
