Aurora Spotted on Brown Dwarf Outside Solar System

Another possibility is that electrically charged particles might rain down on the brown dwarf from above to drive the auroras. 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.

Astronomers announced today (July 29, 2015) that they’ve discovered the first aurora ever seen in an object beyond our solar system.

Like the auroras that lit up the sky here on Earth, these alien ones are essentially stunning displays of color that form in the proximity of the dwarf planet’s poles. Once within the magnetosphere, those particles get accelerated along the planet’s magnetic field lines to the planet’s poles, where they collide with gas atoms in the atmosphere and produce the bright emissions associated with auroras. But brown dwarfs fall short of achieving this internal heat, and so cool and darken from the moment they are born. The light they illuminate is so dim, it can only be observed in the infrared. Yet what really confuses astronomers is how small these stars are – landing somewhere between 15 and 75 times the mass of Jupiter. CREDIT: Chuck Carter and Gregg Hallinan, Caltech.

“Sure enough, we saw it”, Hallinan said.

The bright red auroras of the brown dwarf are that color probably because of the high quantities of hydrogen in its atmosphere.

One way scientists have gone about answering this question is by studying the magnetic activity of brown dwarfs; magnetic fields manifest differently when surrounding a star versus a planet.

Auroral displays result when charged particles manage to enter a planet’s magnetic field. “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”. A new study has found that these attractive, colourful lights can also light up brown dwarfs, often referred to as failed stars. Previously, Hallinan discovered that this dwarf pulses, sending out a blast of radio waves every few hours.

“We already known from observations of brown dwarves that they have clouds in the atmosphere”.

To see if auroras might be seen outside the solar system, astronomers investigated a mysterious Jupiter-size object called LSR J1835+3259, located about 18.5 light-years from Earth. 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. The aurora on LSR J1835+3259 is powered by a little-understood dynamo process.

“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”, said Gregg Hallinan, of the California Institute of Technology. In fact, the aurora that occurs on this so-called “failed star” is almost 10,000 times stronger than those seen elsewhere in space. 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. Burgasser was not involved with the Nature study.

Several large moons orbit inside Jupiter’s magnetosphere including the volcanic moon Io.

Overall, Nichols says the research is exciting because it strengthens the argument that brown dwarfs are more closely related to planets, kind of like “beefed-up Jupiters”.