Too massive to be planets, but too small to ignite the nuclear reactions that characterize stars, brown dwarfs pose a classification problem: What are these hard-to-detect species of unicorns in the universe really?
Now a team of astronomers at the California Institute of Technology (Caltech) has made a discovery that has decisively tipped the balance. The experts have pointed the most powerful radio telescope in the world, the Very Large Array (VLA), and the optical telescopes of the WM Keck Observatory at the brown dwarf LSRJ 1835 + 3259, located 20 light years away, and have been able to verify that, like the Earth and other planets have auroras.
“If you were on the surface of a brown dwarf –something very undesirable due to the extremely high temperatures and the tremendous force of gravity that prevails there–, you would enjoy an incredible light show, courtesy of auroras hundreds of thousands of times more powerful than anyone detected in our solar system ”, explained Gregg Hallinan, director of the research.
This phenomenon occurs when electrically charged particles enter the magnetosphere of a celestial body. The collision of these particles with gas atoms at the poles generates the characteristic emission of light. When they appear on Earth and other planets, it is the solar winds that carry the charged particles, but this would not be the case with brown dwarfs. Scientists believe that the source of their auroras could be planets that orbit them and alter their magnetosphere.
The first clue to the find came in the early 21st century, when astronomers detected that brown dwarfs emitted radio waves. At first they believed that the origin was the same as that of the waves emitted by the stars: the corona, an atmosphere heated to extremely high temperatures by the magnetic activity that is recorded near the surface. But brown dwarfs don’t produce flares like the Sun and other stars.
Later, in 2006, Hallinan found that brown dwarfs emit radio frequency pulses similar to planets in the solar system when they experience auroras. And now he has been able to show that, indeed, it is the same phenomenon.
Image: Chuck Carter and Gregg Hallinan / Caltech
