Caltech: "Failed Stars" Host Powerful Auroral Display

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Caltech: "Failed Stars" Host Powerful Auroral Display

Post by bystander » Wed Jul 29, 2015 10:08 pm

"Failed Stars" Host Powerful Auroral Display
California Institute of Technology | 2015 July 29

Caltech astronomers say brown dwarfs behave more like planets than stars
[img3="Artist conception of an aurora over the polar region of a brown dwarf.
Credit: Chuck Carter and Gregg Hallinan/Caltech
"]https://public.nrao.edu/images/non-gall ... a_nrao.jpg[/img3][hr][/hr]
Brown dwarfs are relatively cool, dim objects that are difficult to detect and hard to classify. They are too massive to be planets, yet possess some planetlike characteristics; they are too small to sustain hydrogen fusion reactions at their cores, a defining characteristic of stars, yet they have starlike attributes.

By observing a brown dwarf 20 light-years away using both radio and optical telescopes, a team led by Gregg Hallinan, assistant professor of astronomy at Caltech, has found another feature that makes these so-called failed stars more like supersized planets—they host powerful auroras near their magnetic poles. ...

"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," says 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."

In the early 2000s, astronomers began finding that brown dwarfs emit radio waves. At first, everyone assumed that the brown dwarfs were creating the radio waves in basically the same way that stars do—through the action of an extremely hot atmosphere, or corona, heated by magnetic activity near the object's surface. But brown dwarfs do not generate large flares and charged-particle emissions in the way that our sun and other stars do, so the radio emissions were surprising.

While in graduate school, in 2006, Hallinan discovered that brown dwarfs can actually pulse at radio frequencies. "We see a similar pulsing phenomenon from planets in our solar system," says Hallinan, "and that radio emission is actually due to auroras." Since then he has wondered if the radio emissions seen on brown dwarfs might be caused by auroras. ...

Astronomers Discover Powerful Aurora Beyond Solar System
National Radio Astronomy Observatory | 2015 July 29

Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence - G. Hallinan et al
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