Runaway Stars Go Ballistic

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LONG BEACH, Calif. — NASA’s Hubble Space Telescope has spotted a total of 14 young stars racing through clouds of gas like bullets, creating brilliant arrowhead structures and tails of glowing gas.

The discovery of the speedy stars by Hubble, announced Jan. 8 at the 213th meeting of the American Astronomical Society here, came as something of a shock to the astronomers who found them.

“We think we have found a new class of bright, high-velocity stellar interlopers,” said study leader RaghvendraSahai of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Finding these stars is a complete surprise because we were not looking for them. When I first saw the images, I said ‘Wow. This is like a bullet speeding through the interstellar medium.'”

The arrowhead structures, or bow shocks, seen in front of the stars are formed when the stars’ powerful stellar winds slam into the surrounding dense gas, like a speeding boat pushing through water on a lake.

The strong stellar winds suggest that the stars are young, just a few million years old, the team concluded. Most stars produce powerful winds either when they are very young or very old; and only very massive stars – with masses greater than 10 times that of the sun – can keep generating these winds throughout their lifetimes.

But the objects Sahai and his team found are not very massive, because they do not have glowing clouds of ionized gas around them. They appear to be medium-sized stars up to eight times more massive than the sun.