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Astronomers find dozens of runaway stars

As water piles up before a ship, so material stacks up ahead of high-mass stars moving fast through space. These cosmic bows shocks revealed the runaway stars.

 Runaway star Zeta Ophiuchi plowing through space dust. The bright yellow curved feature directly above Zeta Ophiuchi is a magnificent example of a bow shock. In this image, the runaway star is flying from the lower right towards the upper left. As it does so, its very powerful stellar wind is pushing the gas and dust out of its way (the stellar wind extends far beyond the visible portion of the star, creating an invisible 'bubble' all around it). And directly in front of the star's path the wind is compressing the gas together so much that it is glowing extremely brightly (in the infrared), creating a bow shock. It is akin to the effect you might see when a boat pushes a wave in front it as it moves through the water. Image credit: NASA

Runaway star Zeta Ophiuchi plowing through space dust. The bright yellow curved feature directly above the star is a bow shock. In this image, the runaway star is flying from the lower right towards the upper left. As it does so, its very powerful stellar wind is pushing the gas and dust out of its way (the stellar wind extends far beyond the visible portion of the star, creating an invisible ‘bubble’ all around it). And directly in front of the star’s path the wind is compressing the gas together so much that it is glowing extremely brightly in the infrared, creating a bow shock. Image via NASA.

In new research, astronomers used images of bow shocks – glowing, arc-shaped features in space – to find dozens of so-called runaway stars, the fastest stars in our galaxy.

Bow shocks are created when speedy, massive stars plow through space and cause material to stack up in front of them in the same way that water piles up ahead of the bow of a ship.

University of Wyoming astronomer William Chick presented the new results yesterday (January 5, 2015) at the American Astronomical Society (AAS) meeting in Kissimmee, Florida. In a statement, Chick said:

Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters. 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, say the researchers, and 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 (24 kilometers per second) relative to its surroundings. (See Zeta Oph’s giant bow shock in the image at the top of the page.)

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 20 times as massive than 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.

View larger. | The speeding stars thought to be creating the bow shocks can be seen at the center of each arc-shaped feature.  The two images at left are from Spitzer, and the one on the right is from WISE. Image credit: NASA/JPL-Caltech/University of Wyoming

View larger. | The speeding stars thought to be creating the bow shocks can be seen at the center of each arc-shaped feature. Cosmic bow shocks occur when massive stars zip through space, pushing material ahead of them. The stars also produce high-speed winds that smack into this compressed material. The end result is pile-up of heated material that glows in infrared light. In these images, infrared light has been assigned the color red. Green shows wispy dust in the region and blue shows stars. The two images at left are from Spitzer, and the one on the right is from WISE. Image credit: NASA/JPL-Caltech/University of Wyoming

The researchers looked at archival infrared data from from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer (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.

The findings suggest that many of the bow shocks are the result of speedy runaways that were given a gravitational kick by other stars. However, in a few cases, the arc-shaped features could turn out to be something else, such as dust from stars and birth clouds of newborn stars. The team plans more observations to confirm the presence of bow shocks.

University of Wyoming astronomer Henry “Chip” Kobulnicky said:

We are using the bow shocks to find massive and/or runaway stars. The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars.

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Bottom line: In new research presented January 5, 2015 at the American Astronomical Society (AAS) meeting in Kissimmee, Florida, astronomers used images of bow shocks – glowing, arc-shaped features in space – to find dozens of so-called runaway stars, the fastest stars in our galaxy.

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Eleanor Imster

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