For the first time, astronomers have detected an aurora erupting beyond the solar system, giving us a profound glimpse at the magnetism surrounding a brown dwarf, or "failed star."
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Until now, the only aurorae astronomers have witnessed have been located on planets within our own star system. The sun produces a steady stream of electrically charged particles, called ions, that wash throughout the solar system as the solar wind and intermittent coronal mass ejections. These ions go on to interact with planetary magnetic fields and atmospheres to generate beautiful lightshows.
In the case of Earth, powerful geomagnetic storms can be triggered when the sun's magnetic field, loaded with ions, interacts with our global magnetosphere. Should this happen, ions from the sun are funneled into higher latitudes, which then interact with our atmosphere, generating Northern and Southern Lights - the Aurora Borealis and Aurora Australis, respectively.
Likewise, aurorae have been observed on Jupiter, Saturn and other planets in the solar system that possess a magnetic field and atmosphere.
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Now astronomers have confirmed the first ever "exo"-aurora, an aurora erupting on a celestial object well beyond the confines of our solar system. But the most fascinating thing about this discovery is that this aurora wasn't detected at an exoplanet, it was detected at a brown dwarf.
"All the magnetic activity we see on this object can be explained by powerful auroras," said Gregg Hallinan, of the California Institute of Technology (Caltech), in a news release. "This indicates that auroral activity replaces solar-like coronal activity on brown dwarfs and smaller objects."
Brown dwarfs are a mysterious class of object that forms a bridge between stars and planets. They possess characteristics of both, but cannot be clearly defined as either. As they are lower mass objects than stars that maintain nuclear fusion in their core, brown dwarfs are often referred to as "failed stars" - they are not massive enough to sustain fusion for long periods of time.
But what brown dwarfs lack in the fusion department, they certainly seem to make up for in the aurora department; the aurora detected on brown dwarf LSR J1835+3259 is 10,000 times more powerful than any planetary aurora we have detected previously.
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LSR J1835+3259 is located 18 light-years from Earth and the radio signal generated by its aurora was detected by the Karl G. Jansky Very Large Array (VLA) in New Mexico. Optical measurements of the brown dwarf by the 5-meter Hale Telescope on Palomar Mountain, Calif., and the 10-meter Keck Telescope in Hawaii were also able to characterize the object. These observations have found that brown dwarfs support extremely powerful auroral activity, much stronger than planetary magnetic fields, but weaker than the coronal magnetic activity that can be found in more massive stars like our sun.
This discovery is exciting, not only in the field of brown dwarfs, but also in understanding planetary dynamics and exoplanetary studies. It appears that brown dwarf aurorae are powered by a dynamo process that is poorly understood and yet has also been observed in aurorae erupting on the largest planets in our solar system.
"What we see on this object appears to be the same phenomenon we've seen on Jupiter, for example, but thousands of times more powerful," Hallinan added. "This suggests that it may be possible to detect this type of activity from extrasolar planets, many of which are significantly more massive than Jupiter."