An international team of astronomers observed some unusual radio signals coming from a nearby red dwarf star. It turns out that the radio waves were being produced by the interaction of an exoplanet orbiting the star, causing the red dwarf to have aurorae. Despite this having been predicted for over thirty years, this is the first time that astronomers have been able to actually see this signal.
On June 16, 2016, astronomers spotted the intriguing signal coming from GJ1151, an ordinary red dwarf situated 26 light-years away in the constellation Ursus Major. Stars give off all sorts of electromagnetic signals, but low frequencies have not been studied in detail before. After ruling out various possibilities, the researchers are confident the only explanation is the interaction between the star and a planet. The findings are reported in Nature Astronomy.
This observation is an interesting new step in the detailed study of the properties of exoplanets in these systems. Red dwarfs are the most common types of star in the Milky Way. They are much cooler and smaller than the Sun but have stronger magnetic fields. Many known red dwarfs are orbited by Earth-size planets, and as these planets orbit, they can create peculiar magnetic interactions. Now, at last, we can detect them.
"The motion of the planet through a red dwarf’s strong magnetic field acts like an electric engine much in the same way a bicycle dynamo works. This generates a huge current that powers aurorae and radio emission on the star," lead author Dr Harish Vedantham, from the Netherlands Institute for Radio Astronomy (ASTRON), explained in a statement.
Something along these lines is also visible in the Solar System, but not from the Sun. A similar interaction happens between Jupiter, which has a very strong magnetic field, and its volcanic moon Io. These interactions are brighter than the Sun itself in some particular low radio frequencies.
"We adapted the knowledge from decades of radio observations of Jupiter to the case of this star," said co-author Dr Joe Callingham, ASTRON postdoctoral fellow. “A scaled-up version of Jupiter-Io has long been predicted to exist in the form of a star-planet system, and the emission we observed fits the theory very well.”
The observations were possible thanks to the Dutch-led Low-Frequency Array (LOFAR) radio telescope. The team is now looking at more red dwarfs to see how common this phenomenon is. LOFAR is expected to find at least another 100 of these systems in the solar neighborhood, and future observatories such as the Square Kilometer Array may be able to find even more.
“The long-term aim is to determine what impact the star’s magnetic activity has on an exoplanet’s habitability, and radio emissions are a big piece of that puzzle,” explained Dr Vedantham. “Our work has shown that this is viable with the new generation of radio telescopes, and put us on an exciting path.”