Brown Dwarf Stars Can Host Powerful Aurora Displays

Posted on July 30, 2015

Astronomers have determined that brown dwarf stars can host powerful aurora displays like the Northern Lights on Earth. Brown dwarf stars are also called failed stars. They are difficult to classify because they are too massive to be planets yet they have characteristics of planets, such as being too small to sustain hydrogen fusion reactions at their cores.

Gregg Hallinan, assistant professor of astronomy at Caltech and leader of the research team, says in a statement, "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. 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."

Hallinan and the team of astronomers from the Universities of Sheffield and Oxford observed a brown dwarf called LSRJ 1835+3259 using the National Radio Astronomy Observatory's Very Large Array (VLA). They detected a bright pulse of radio waves that appeared as the brown dwarf rotated. Using the Hale Telescope the researchers then observed that the brown dwarf varied optically on the same period as the radio pulses. The researchers also found that the object's brightness varied periodically by focusing on its h-alpha emission line. Next the researchers used the Keck telescope to observe the brown dwarf's brightness over time. Using the data they collected they were able to confirm that the hydrogen emission is a signature of auroras near the surface of the brown dwarf.

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

Here is a video showing the brown dwarf pulsing as with the National Radio Astronomy Observatory's Very Large Array.

A research paper on the findings was published here in the journal, Nature.



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