Brown Dwarf Auroras Make Them More Planet-Like Than Ever
Astronomers have found the first aurora outside our solar system on a brown dwarf. This makes these confusing objects, which have both planetary and stellar characteristics, more planet-like than ever before.
A Brown dwarf is a very ambiguous thing. They are substellar objects that are too big to be planets but are relatively small and don’t fuse hydrogen, so they are not stars either.
Yet they can have characteristics that are quite star-like and quite planet-like at the same time.
For example, they form from immense collapsed clouds of hydrogen gas and dust and are classified by their spectral-type like stars. Some fuse elements like deuterium (an isotope of hydrogen) for a small part of their lives.
On the other hand, their masses are closer to large planets than they are to many stars. They emit radio waves more like some planets do as well. They also have cloudy atmospheres.
And now there’s one more thing they do like planets. They have auroras.
No, I’m not talking about those elite magicians in the Harry Potterverse. Auroras are among the most dazzling visual displays the earth has to offer. They are caused by charged particles from the sun being funneled by earth’s magnetosphere down to the poles where they strike atoms in the atmosphere. This collision imparts energy to the atoms causing some of the electrons to shift into a higher (more energetic) orbit. When the electrons move back to their proper orbits, they release energy as light that we see as beautiful shimmering curtains of light.
Astronomers at the California Institute of Technology led by astronomer Gregg Hallinan recently detected auroras on a high-mass brown dwarf 20 light years away called LSR J1835+3259. Using a suite of earth-bound optical and radio telescopes, they looked for previously detected blasts of radio waves. Such radio waves have been detected from Jupiter and were associated with Jupiter’s auroras. Perhaps this dwarf had auroras as well. And boy did it. They’re at least 10 million times as powerful as those we see from earth. But how are they created? There is no nearby real star to supply the required charged particles. Astronomers think they may come from an orbiting planet that sends the particles into the dwarf’s magnetosphere.
So now we have yet more evidence that Brown dwarfs are not just stars that didn’t make the grade. Gregg Hallinan said:
“Brown dwarfs span the gap between stars and planets and these results are yet more evidence that we need to think of brown dwarfs as beefed-up planets, rather than “failed stars”.
Perhaps we should call these things what some astronomers wanted to call them before they settled on brown dwarfs. A planetar.
Either way, I’d love to visit this world and see an aurora that’s millions of times more impressive than anything we have on earth. Being crushed down to the size of a sugar cube by the immense gravity might be worth it.
Image Credit: Chuck Carter and Gregg Hallinan, Caltech