"The stars are like rocks in a rushing river," said Matt Povich of the University of Wisconsin, Madison. "Powerful winds from the most massive stars at the center of the cloud produce a large flow of expanding gas. This gas then piles up with dust in front of winds from other massive stars that are pushing back against the flow." Povich is lead author of a paper describing the new findings in the Dec. 10 issue of the Astrophysical Journal. (Photo above is an infrared view of the Swan nebula and is courtesy of NASA/JPL-Caltech/Univ. of Wisc.)
Spitzer's new infrared view of the stormy region, called M17, or the Swan nebula, is online at this direct link. The Swan is located about 6,000 light-years away in the constellation Sagittarius. Dominating the center of the Swan is a group of massive stars, some exceeding 40x the mass of our sun. These central stars are 100,000 to one million times as bright as the sun and roar with radiation and fierce winds comprised of charged particles that speed along at up to 7.2 million kilometers per hour (4.5 million miles per hour). Both the wind and radiation carve out a deep cavity at the center of the picture -- an ongoing process thought to trigger the birth of new stars. The growth of this cavity pushes gas up against winds from other massive stars, causing "smiley-faced" bow shocks -- three of which can be seen in the new picture. The direction of the bow shocks tells researchers exactly which way the "wind is blowing."
"The bow shocks are like interstellar weather vanes, indicating the direction of the stellar winds in the nebula," said Povich who, with his colleagues, also used Spitzer to take an infrared picture of a star-forming region called RCW 49. Spitzer was able to spot the bow shocks because its infrared eyes can pierce intervening dust, and because it can photograph large swaths of sky quickly. Ultimately, the new observations will help researchers understand how solar systems like our own are able to form and persist in the rough, celestial seas of space.