Brown dwarfs often get a bad rap for being "failed stars" or "sub-stellar objects," but in light of new research they may finally be known as "over-achieving planets." Scientists have used a radio antenna array in Europe to detect evidence that some brown dwarfs may glow with powerful aurorae.
We know an aurora as the beautiful and sometimes dramatic glow that appears at high latitudes when the sun's highly-charged particles interact with our planet's global magnetosphere. The solar wind and explosive events like coronal mass ejections (CMEs) will carry solar plasma (primarily energetic protons) out to the Earth's orbit. Often, they will interact with the geomagnetic field and spiral down toward the poles (where the magnetic field is directed). On interacting with the atmosphere, light is generated, producing the aurora we know and love.
However, before the particles are absorbed by the atmosphere, creating auroral light, spiraling plasma will generate radio emissions that can be detected. It stands to reason that any planetary body with a global magnetic field should have their own aurorae and also generate a radio hum. Indeed, astronomers are very familiar with aurorae on Jupiter and Saturn - Jovian auroral displays known to be 100 times more intense than anything Earth's atmosphere can generate and their associated radio emissions can be studied.
But what about exoplanets and brown dwarfs? Can their aurorae also be detected?
Jonathan Nichols and his University of Leicester team have deduced that the radio emissions generated by auroral processes on Jupiter can also be detected over interstellar distances, potentially providing astronomers with a means to detect magnetospheres on distant alien worlds.
"We have recently shown that beefed-up versions of the auroral processes on Jupiter are able to account for the radio emissions observed from certain "ultracool dwarfs" - bodies which comprise the very lowest mass stars - and "brown dwarfs" - ‘failed stars' which lie in between planets and stars in terms of mass," Nichols said in a press release. "These results strongly suggest that auroras do occur on bodies outside our solar system, and the auroral radio emissions are powerful enough - one hundred thousand times brighter than Jupiter's - to be detectable across interstellar distances."
These exciting results were acquired by using the Low Frequency Array (LOFAR) that is centered in the Netherlands with sites distributed over the UK and northern Europe.
The detection of brown dwarf aurorae (and, by extension, aurorae on large exoplanets) can provide novel measurements of the object's rotation, magnetic field strength, stellar interactions and whether or not the object has anything in orbit around it.
As previously reported on Discovery News, the detection of exoplanetary magnetospheres through their radio emissions could potentially aid the search for habitable worlds and alien life.
Image: Artist's impression of an aurora on an exoplanet. Credit: David A. Aguilar (CfA)