Scientists have used the world’s most powerful radio telescope to uncover evidence of hidden planets orbiting distant stars, opening up a new avenue in the search for extraterrestrial life.
Since the first exoplanet was discovered in the 1990s, the search for other planets outside our solar system has mostly used optical telescopes.
However researchers in the Netherlands have used the Low Frequency Array (LOFAR), a massive radio telescope three kilometres across, to find stars that have planets orbiting them which give off unique radio frequencies.
The team found 19 distant red dwarf stars that gave off a distinctive radio signature, suggesting at least four of them had orbiting planets that were generating the radio waves.
University of Queensland astrophysicist Benjamin Pope was part of the team analysing the data and led the group that compared it with optical telescope data from the same area of the sky.
Dr Pope said the sun and even the Earth gave off radio waves, but Jupiter gave a good local example of what was happening.
“The signals they are giving off are exactly what Jupiter looks like at these radio frequencies, and the reason it looks like that is because it’s magnetically connected to its innermost moon Io, and Io goes whipping around in its magnetic field like a generator,” he said.
“What we think is happening around these stars is they’re a scaled up version of that, where the star is Jupiter and the planet is Io.”
Previously there was too much background noise in that particular range of low-frequency radio waves to get much usable data, but the research team had a breakthrough in realising such star-planet systems would give off highly polarised radio waves.
“It’s like putting on polarised sunglasses, almost literally like that, to filter out the glare,” Dr Pope said.
“All the radio noise from black holes, stars, planets and the like or not polarised at all, so if you just look for polarised sources then the very few, very rare sources actually stick out.”
Unfortunately for a scientist such as Dr Pope, who looks for exoplanets that could support life, the very thing that makes the planetary systems stick out is the thing that makes them unlikely to harbour life.
The Earth is protected by its own magnetic field, which shields us from much of the radiation thrown off by the sun, however these planets have a magnetic link with their star, meaning the radiation would stream onto their surface.
The researchers also stress that while the findings strongly indicated the type of planet-star model they describe, they were unable to confirm this using conventional optical telescopes, as red dwarf stars are typically too faint to allow that type of observation.
Despite this, Dr Pope said the finding was a huge breakthrough.
“Every time we open a new window on the universe – a new telescope, a new wavelength – we find new things,” he said.
“This is a whole new tool in the arsenal of exoplanet observers, where in the past we’ve been limited to looking in the optical and infrared bands so far.”
The research has been published in the journals Nature Astronomy and Astrophysical Journal Letters.