Mysterious radio signals may be coming from undiscovered planets


Astronomers have discovered strange radio signals that could be coming from unseen planets. Models suggest that some of the signals could be produced through interactions between the magnetic fields of planets and their host stars, which could represent a brand new way to detect exoplanets.

So far, more than 4,500 exoplanets have been detected orbiting other stars. Most of them are spotted using the transit method, which relies on the light from a star dimming slightly as a planet passes in front of it. Radial velocity is another common technique, where astronomers watch for a star wobbling from the gravitational influence of orbiting exoplanets. Other methods are emerging too, such as gravitational microlensing.

And now we may have a new technique in the toolbox. Astronomers from ASTRON, the national observatory of the Netherlands, and the University of Queensland in Australia have been experimenting with detecting planets through radio waves, using the Low Frequency Array (LOFAR) telescope.

The team was examining red dwarfs; small stars with strong magnetic activity that produces flares and radio emissions. Detecting these stars was an advance in itself, because at greater distances from Earth, space becomes quite radio-loud, and it’s tricky to separate individual objects. But LOFAR’s increased sensitivity allowed the astronomers to pick up 19 red dwarf stars.

Of those, four were particularly intriguing – they were older stars with reduced magnetic activity, meaning they “shouldn’t” have popped up in the survey. When the astronomers modeled what could be creating the radio signals, the best explanation was that the stars were being orbited by hidden planets.

Stars give off huge amounts of material and charged particles, collectively called the stellar wind. When this interacts with the magnetic field of planets, it can produce aurorae and radio waves, especially if the planet is blasting its own material into space. This kind of interaction can be seen in our own solar system between Jupiter and its moon Io, and the team says that it’s the best fit for the radio signals from these four strange red dwarfs.

“Our model for this radio emission from our stars is a scaled-up version of Jupiter and Io, with a planet enveloped in the magnetic field of a star, feeding material into vast currents that similarly power bright aurorae,” says Joseph Callingham, lead author of the study. “It’s a spectacle that has attracted our attention from lightyears away.”

For now, any planets that may be orbiting these stars have yet to be directly discovered or confirmed, but the model is intriguing enough to look. The team says that future radio telescopes could be sensitive enough to spot them, and if confirmed, the technique could join our repertoire for detecting exoplanets.

The research was published in two papers, appearing in Nature Astronomy and the Astrophysical Journal Letters.

Source: University of Queensland