"Renegade" Stars Tearing Across Universe, Hubble Shows

Anne Minard in Long Beach, California
National Geographic News
January 8, 2009

Ripples in cosmic gas that resemble speedboat wakes have revealed a new population of young, renegade stars barreling through the universe at more than 112,000 miles (180,250 kilometers) an hour.

The stars appear to be just a few million years old and a few times larger than the sun.

As they careen through the cosmos, the stars' winds slam against nearby gas, creating enormous bow shocks billions or even a trillion miles wide.

So far astronomers have found 14 of these rogue stars using images from the Hubble Space Telescope.

But study leader Raghvendra Sahai, of NASA's Jet Propulsion Laboratory in Pasadena, California, thinks the stellar interlopers will turn out to be common in the universe.

Sahai unveiled his results Wednesday at the American Astronomical Society meeting in Long Beach, California.

The Flying Wedge

Sahai and colleages discovered the odd stars while peering at images taken between October 2005 and July 2006. They were looking for what they thought was a subclass of dying stars near the Milky Way's galactic plane, the flattened region where most of the galaxy's stars lie.

Sahai's team found objects that shared some of the same characteristics of the dying stars they sought, but closer inspection revealed 14 of the 38 suspect objects as stellar renegades instead.

"We accidentally stumbled across a new class of objects," Sahai said.

(Related photo: "Milky Way's Turbulent Core in Hi-Res" [January 6, 2008].)

The stars may be the ousted members of two-star systems that were ejected when their partners exploded as supernovae.

It's also possible that a binary star system would collide with another binary set or a single star and the interaction would fling one of the stars into space.

In either scenario, the ousted stars go shooting away to follow their own unique paths, Sahai said.

Based on the shapes of the wakes, the researchers have dubbed the strange objects with names such as "The Flying Wedge," "The Whirlygig," and "The Cropduster."

Tip of the Iceberg

Runaway stars have been spotted once before, with the Infrared Astronomical Satellite in 1983. But those stars are believed to be much more massive than the ones found by the Hubble team.

"We think the massive runaway stars observed before were just the tip of the iceberg," Sahai said in a statement.

The group is planning future studies using the Arizona Radio Observatory's 10- and 12-meter telescopes, and the National Radio Astronomy Observatory's radio arrays in New Mexico and West Virginia.




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