Forget hurricane Irene that hammered the U.S. East Coast last month. You can even forget the monster storm whirling endlessly on Jupiter, creating the famous Great Red Spot. If celestial objects could compare storm violence, a nearby brown dwarf would win easily — and its effects can be detected 47 light-years away.
The brown dwarf in question, called “2MASS J21392676+0220226″ (a.k.a. “2MASS 2139″), was studied by a University of Toronto team of astronomers using an infrared camera attached to the 2.5 meter telescope at Las Campanas Observatory in Chile. They discovered something rather perplexing about this “failed star.”
Over a short observational period of a few hours, the researchers noticed 2MASS 2139 change in brightness significantly. Naturally, that piqued their interest.
“We found that our target’s brightness changed by a whopping 30 percent in just under eight hours,” said postgraduate Jacqueline Radigan, lead author of the publication that has been submitted to the Astrophysical Journal. The work of Radigan’s team will also be presented at the Extreme Solar Systems II conference in Jackson Hole, Wyoming this week.
So what could be causing these brightness variations? After all, a brown dwarf doesn’t have surface features like bright ice caps and dark lava flows that one would expect on the solid surface of a rocky planet.
Brown dwarfs are sub-stellar objects that are too small to ignite long-term fusion in their cores (therefore they’re not stars) and they don’t exhibit chemical differentiation by height (therefore they’re not planets). Brown dwarfs are rather mysterious in that they exist in a stellar hinterland, bridging the gap between the largest planets and the smallest stars.
If the observed brightness changes aren’t caused by surface features (as there’s no “surface”), what could it be?
“The best explanation is that brighter and darker patches of its atmosphere are coming into our view as the brown dwarf spins on its axis,” said Radigan.
Co-author Ray Jayawardhana, Canada Research Chair in Observational Astrophysics at the University of Toronto, agrees: “We might be looking at a gigantic storm raging on this brown dwarf, perhaps a grander version of the Great Red Spot on Jupiter in our own solar system, or we may be seeing the hotter, deeper layers of its atmosphere through big holes in the cloud deck.”
We may not be able to observe brown dwarfs up-close, but extensive theoretical models have been used to simulate their atmospheres — cloud formation is all part of the equation. Grains of silicate and metal dust are thought to be present in brown dwarfs’ atmospheres, and when they condense, clouds form.
As for 2MASS 2139, it appears that extensive brown dwarf-wide storms are violently distorting its atmosphere, producing a fluctuating infrared signal as it rotates. Understanding the physics behind these storms will provide invaluable data, helping us better understand the link between planetary and brown dwarf atmospheres.
Image credit: Jon Lomberg/Univ. of Toronto