Image courtesy J. Walsh and Z. Levay, ESA/NASA
Published May 11, 2010
A stellar speed demon racing away from its home may be a never before seen type of runaway star, astronomers have announced.
Dubbed 30 Dor 016, the massive star is whipping through space at a record-breaking 250,000 miles (400,000 kilometers) an hour. The fugitive already appears to have traveled 375 light-years from its birthplace: a star cluster called R136 deep in the Tarantula Nebula.
The team chose the star as a target to help calibrate the newly installed Cosmic Origins Spectrograph (COS), an instrument designed to look at the light signatures—or spectra—of very distant, faint objects.
After looking at the light coming from 30 Dor 016, the scientists "knew immediately that it was a massive star that had stellar winds blowing at breakneck speeds," said study co-author Danny Lennon, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland.
"Given that the mass of the star is proportional to the velocity of the material being expelled, we knew right away that its wind was the fastest ever seen."
Such powerful wind means that the star is incredibly massive: Lennon and colleagues calculate that the runaway is roughly 90 times the mass of our sun.
Runaway Star Kicked Out of the "Dance"?
Astronomers first caught a glimpse of 30 Dor 016 in 2006, when a team in Australia classified the star as a hot, blue-white rebel that was surpisingly far from any known clusters.
The recent Hubble data revealed the misfit to be a young runaway, likely no more than a few million years old, since very massive stars have relatively short life spans.
In addition, archived Hubble pictures made with visible light show that the star lies in a cavity being carved by its sprint through the nebula. The cavity's shape suggests that the star is traveling away from the R136 cluster. (Related: "Hubble Telescope at 20: NASA Astronomers' Top Photos.")
According to theory, there are two main ways stars can get booted out of their home clusters. A nearby supernova can give the star a kick, or a complex gravitational dance between neighboring stars—called dynamical interaction—can send a star packing.
The R136 cluster is thought to be no more than two million years old, which means it's far too young for any supernova to have occurred yet, said Raghvendra Sahai, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, California, who wasn't involved in the study.
Instead, study co-author Lennon said, "we think that a massive star has essentially interacted with a massive binary pair of stars" in a cosmic version of billiard balls. "This then caused one of the stars to get ejected in a slingshot effect."
Stars ejected by supernovae have been seen before, but 30 Dor 016 is the first known candidate for a star that's been kicked out of a "dance party," the study authors report in a paper published online May 5 in the Astrophysical Journal Letters.
The runaway won't get too much farther, though. Given its size and current age, the star should go supernova sometime within the next half million years.
Runaway a Clue to Fabled Stellar Titans
According to JPL's Sahai, "if we believe the authors' argument that [30 Dor 016] is a runaway star and that it has been ejected from R136, then it is a very valuable discovery of the process of dynamical interaction."
Understanding dynamical interaction can give researchers new insight into the early days of the universe.
That's because, in addition to booting a few youngsters, such cosmic billiard games might cause stars that don't leave the nest to collide and merge into supermassive stars, computer models hint.
These theoretical titans could grow to be as much as 150 to 300 times the sun's mass. Such giants are thought to have been common in the early universe, so Lennon and his team hope to use Hubble to track down modern versions of the fabled monsters.
"If we can find these supermassives," Lennon said, "then it makes the Tarantula Nebula and its cluster a unique laboratory for testing the kinds of stars that formed just after the big bang."
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