'Northern Lights' Aurora Spotted on Distant Brown Dwarf Outside Our Solar System

It turns out that brown dwarfs are a lot more like planets than stars. While these objects are too massive to be considered planets, they're too small to sustain hydrogen fusion reactions at their core. Now, scientists have taken a closer look at brown dwarfs to find out a bit more about them.

"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 Gregg Hallinan, one of the researchers, in a news release. "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 heated by magnetic activity near the star's surface. Brown dwarfs, though, 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.

Instead, we see a similar phenomenon on planets. Auroral displays result when charged particles, carried by the stellar wind, manage to enter a planet's atmosphere, the region where these particles are influenced by the planet's magnetic field. Once within the magnetosphere, those particles are accelerated along the planet's magnetic fields lines to the planet's poles, where they collide with gas atoms in the atmosphere and produce the bright emissions associated with auroras.

"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 Hallinan. "We now know that this kind of auroroal behavior is extending all the way from planets up to brown dwarfs."

The findings are published in the journal Nature.

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