Intense auroral emissions from the universe’s tiniest stars may provide a new way to hunt for rocky planets that might otherwise go unseen. As a world moves through the magnetic field of its star, it can produce bursts of radio waves. The effect is akin to one astronomers have closely studied right here in the solar system: periodic radio emissions made by interactions between Jupiter and its moon Io. Using a powerful radio telescope, researchers have now identified multiple stars emitting the telltale activity. Each one, they say, could be host to a small world.
As a star rotates, its magnetic field sweeps through space, interacting with the charged particles blown from the stellar surface and carried away by stellar wind. If a planet orbits very close to the rotating star, it can further accelerate those particles, causing a bright flash in low-frequency radio waves. Such flashes are readily detectable in data from the Low Frequency Array (LOFAR), a European radio telescope network operating at the lowest frequencies that can be observed from Earth. LOFAR is in the midst of taking a wide-field, low-frequency radio survey, scanning the sky for sources. Parsing through the first data release from 2019, which encompassed about a fifth of the Northern Hemisphere sky, researchers flagged suspicious radio flashes from 19 red dwarf stars. Flashes from five of the stars were initially identified as closely matching predictions for how a planet’s auroral fireworks should look when witnessed from light-years away. Those results appear in a study published in Nature Astronomy, and a subsequent preprint paper has narrowed the candidates to four stars.
“We see no trends that we would expect if the emission was driven by stellar activity,” says the Nature Astronomy study’s lead author Joseph Callingham, a radio astronomer at Leiden University in the Netherlands. All four stars are relatively quiescent, meaning they are unlikely to constantly emit large flares that could mimic an auroral signal from a close-orbiting world.
For years, astronomers have been hunting for signs of planets interacting with the magnetic fields of their stars, focusing on the small subsets of suns thought to be most conducive for the search. Rather than targeting specific stars, however, Callingham and his colleagues relied on LOFAR’s blind, catch-all sky survey, allowing a mor