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Alien dwarf 'star' flashes her dazzling brown rear at stunned space boffins

You won't see that headline in Nature

Video Astronomers have spotted a brown dwarf almost-star glowing with a dazzling display of aurora similar to the Northern Lights and Southern Lights here on Earth – but hundreds of thousands of times brighter.

A team led by Caltech has been focusing telescopes on LSRJ 1835+3259, a brown dwarf sorta-planet 20 light years from Earth, and caught bright flashes coming from the body and bursts of radio activity. This might have been generated in the same way suns do, from magnetic activity on the surface, but according to these new findings, published in the journal Nature, the emissions are actually aurora.

"As the electrons spiral down toward the atmosphere, they produce radio emissions, and then when they hit the atmosphere, they excite hydrogen in a process that occurs at Earth and other planets, albeit tens of thousands of times more intense," said Gregg Hallinan, assistant professor of astronomy at Caltech. "We now know that this kind of auroral behavior is extending all the way from planets up to brown dwarfs."

Brown dwarfs are astronomical oddities – massive gas giants that almost make the critical mass to become star, but not quite. Their existence was predicted long before astronomers actually spotted one in 1994, but debate has raged as to whether they are more like planets than stars.

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The team used the National Radio Astronomy Observatory's Very Large Array (VLA) radio telescope and optical systems, including Palomar's Hale Telescope and the W. M. Keck Observatory, to check the findings and observe the brown dwarf's flares, showing that they exhibited behavior most commonly seen on planets.

"We're finding that brown dwarfs are not like small stars in terms of their magnetic activity; they're like giant planets with hugely powerful auroras," said Hallinan. "If you were able to stand on the surface of the brown dwarf we observed – something you could never do because of its extremely hot temperatures and crushing surface gravity – you would sometimes be treated to a fantastic light show courtesy of auroras hundreds of thousands of times more powerful than any detected in our solar system."

But brown dwarfs are generally wanderers that don't orbit a star. With no solar-generated charged particles to ignite the reaction, the team suspects that a planet moved through its magnetosphere to cause the display.

Brown dwarfs are of particular interest to planetary scientists because they might tell us something about the features found in exoplanets, the massive bodies orbiting stars currently being cataloged by the Kepler space telescope.

These exoplanets are, however, somewhat obscured by the light of the suns they orbit. Brown dwarfs don't have this problem, and so make good candidates for study to see what an exoplanet might be like structurally, and in particular the magnetosphere that is key to auroral displays.

"That could be particularly interesting because whether or not a planet has a magnetic field may be an important factor in habitability," Hallinan said. "I'm trying to build a picture of magnetic field strength and topology and the role that magnetic fields play as we go from stars to brown dwarfs and eventually right down into the planetary regime." ®

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