Dec. 11, 2007 -- A teensy, dim star just 35 light-years from Earth has startled astronomers by being something of a stellar freak.
Instead of being very simple, relatively cool and quiet, the M-dwarf star TVLM513-46546 in the constellation Bootes has shown itself to be strangely magnetic and spinning very fast. It also has an odd and persistent hot spot covering one hemisphere and a bit of a flaring temper.
"It's a much more complex system than anyone expected," said astronomer Edo Berger, a Carnegie Institution-Princeton University fellow.
Berger is on the team of researchers who have taken a look at the seemingly boring little star -- only 8 to 10 percent the mass of the sun and only a small fraction as bright -- with four very different and powerful telescopes to see it in unprecedented detail. Their results will be published in the Feb. 10, 2008 issue of The Astrophysical Journal.
The four telescopes were the radio wave-seeing Very Large Array (VLA) in New Mexico, the optical light-seeing Gemini North telescope, the ultraviolet-seeing Swift space observatory and NASA's Chandra X-ray Observatory.
"If the sun had flares like this (star's)," Berger said, "life would be different here."
It was the need to dissect those flares that made it so important to look at the dwarf star in many wavelengths at the same time, Berger said. As with solar flares, the explosive events start with tangled magnetic fields, which are detectable with radio waves.
Then there's a flash of X-rays and changes in optical and ultraviolet light as the flare propagates out of the star. Only by watching the star simultaneously with all those telescopes can a flare be sorted out.
Such observations had not been done before, Berger explained, because most astronomers doubted there would be much to see: just a dim, cool little star that didn't do much. That changed a few years ago when some astronomers pointed the Chandra X-ray telescope at it.
"We found no X-rays emissions except for a bright flare," said Lars Bildsten, a professor of theoretical physics at the University of California at Santa Barbara. "That was a real shock."
Magnetic fields and flares are supposed to come from a "shear zone" inside stars where the inner core is in contact with a more fluid outer portion -- which rotate at different speeds. The differences in speed generate the magnetism, which can propagate outwards as tangled knots of energy and pop as flares. At least that's the story for sun-like stars.
Dim dwarf stars, however, were not expected to have a shear zone inside them, said Bildsten. They were supposed to be convecting -- like a boiling pot -- from core to surface as low-level nuclear fusion kept them barely lit. This low-level fusion, which slowly converts hydrogen to helium, is also expected to allow these M-dwarf stars to live a very long time -- as long as the universe.
It looks like that assumption was wrong, the researches say. What's more, despite the strangeness of TVLM513-46546, it's probably not all that different from other M-dwarfs.
"They are more different than the sun then we expected," said astrophysicist Ansgar Reiners of Germany's Georg-August-Universitat in Gottingen. "I think we are in a phase that we're just trying to see what's out there."
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