Radio signals from distant stars may suggest hidden planets, researchers say

Scientists have discovered stars unexpectedly blasting out radio waves, possibly indicating the existence of hidden planets.

Researchers have been searching for planets using the world’s most powerful radio telescope, Low Frequency Array (LOFAR), in the Netherlands.

In the past, only the very nearest stars in steady radio emission could be detected, and everything else in the radio sky was interstellar gas, or exotica such as black holes.

But now radio astronomers are able to see plain old stars when they make their observations.

Using that information, they can search for any planets surrounding those stars.

Dr Benjamin Pope, of the University of Queensland, Australia, said: “We’ve discovered signals from 19 distant red dwarf stars, four of which are best explained by the existence of planets orbiting them.

“We’ve long known that the planets of our own solar system emit powerful radio waves as their magnetic fields interact with the solar wind, but radio signals from planets outside our solar system had yet to be picked up.

“This discovery is an important step for radio astronomy and could potentially lead to the discovery of planets throughout the galaxy.”

The researchers focussed on red dwarf stars, which are much smaller than the Sun and are known to have intense magnetic activity that drives stellar flares and radio emission.

However, researchers say some old, magnetically inactive stars also showed up, challenging conventional understanding.

Dr Joseph Callingham, at Leiden University, and at the Dutch national observatory, Astron, is the lead author of the research.

Dr Callingham said that the team is confident these signals are coming from the magnetic connection of the stars and unseen orbiting planets, similar to the interaction between Jupiter and its moon, Io.

He added: “Our own Earth has aurorae, commonly recognised here as the northern and southern lights, that also emit powerful radio waves – this is from the interaction of the planet’s magnetic field with the solar wind.

“But in the case of aurorae from Jupiter, they’re much stronger as its volcanic moon Io is blasting material out into space, filling Jupiter’s environment with particles that drive unusually powerful aurorae.

“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.

“It’s a spectacle that has attracted our attention from light years away.”

Dr Pope concluded: “We can’t be 100% sure that the four stars we think have planets are indeed planet hosts, but we can say that a planet-star interaction is the best explanation for what we’re seeing.

“Follow-up observations have ruled out planets more massive than Earth, but there’s nothing to say that a smaller planet wouldn’t do this.”

The findings are published in Nature Astronomy.