Bow shocks thought to mark the paths of massive, speeding stars are highlighted in these images from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE. Credit: NASA/JPL-Caltech/University of Wyoming
Astronomers are finding dozens of the fastest stars in our galaxy with the help of images from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE. When some speedy, massive stars plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship. Called bow shocks, these dramatic, arc-shaped features in space are leading researchers to uncover massive, so-called runaway stars.
“Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters,” said astronomer William Chick. “The gravitational boost increases a star’s speed relative to other stars.” Our own sun is strolling through our Milky Way galaxy at a moderate pace. It is not clear whether our sun creates a bow shock. By comparison, a massive star with a stunning bow shock, called Zeta Ophiuchi (or Zeta Oph), is traveling around the galaxy faster than our sun, at 54,000 mph relative to its surroundings.
Both the speed of stars moving through space and their mass contribute to the size and shapes of bow shocks. The more massive a star, the more material it sheds in high-speed winds. Zeta Oph, which is about 20X as massive as our sun, has supersonic winds that slam into the material in front of it. The result is a pile-up of material that glows. The arc-shaped material heats up and shines with infrared light. That infrared light is assigned the color red in the many pictures of bow shocks captured by Spitzer and WISE.
Chick and his team turned to archival infrared data from Spitzer and WISE to identify new bow shocks, including more distant ones that are harder to find. Their initial search turned up more than 200 images of fuzzy red arcs. They then used the Wyoming Infrared Observatory, near Laramie, to follow up on 80 of these candidates and identify the sources behind the suspected bow shocks. Most turned out to be massive stars. Many of the bow shocks are due to speedy runaways that were given a gravitational kick by other stars. But in some cases the arc-shaped features could turn out to be dust from stars and birth clouds of newborn stars.
Some of the first bow shocks from runaway stars were identified in the 1980s by David Van Buren of NASA’s JPL. He and his colleagues found them using infrared data from the Infrared Astronomical Satellite (IRAS), a predecessor to WISE that scanned the whole infrared sky in 1983. http://www.jpl.nasa.gov/news/news.php?feature=4812
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