Using the world’s most powerful radio telescope, LOFAR, scientists have discovered stars unexpectedly blasting out radio waves, possibly indicating the existence of hidden planets.

Published by the editorial team, 11 October 2021

Searching for red dwarfs

Leiden University’s Dr Joseph Callingham and his colleagues have been searching for aurorae from exoplanets using the Low Frequency Array (LOFAR), the world’s most powerful radio telescope. “We’ve discovered signals from 19 distant red dwarf stars, four of which are best explained by the existence of planets orbiting them,” Dr Callingham said. “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. This same process drives the beautiful aurorae we see at the poles of Earth.

This is an image that reflects the work of ASTRON.
Artist impression of a red-dwarf star’s magnetic interaction with its exoplanet. Credit to image: Danielle Futselaar (artsource.nl)

“However, it is only with LOFAR have we had the sensitivity to find auroral emission outside our Solar System. This is an incredibly powerful tool to help find planets outside our Solar System and to determine their magnetic fields.” LOFAR was designed, built and is presently operated by ASTRON, the Netherlands Institute for Radio Astronomy, its core is situated in Exloo, the Netherlands.

A spectacle from lightyears away

Dr Harish Vedantham at ASTRON, the Netherlands Institute for Radio Astronomy, co-author of the paper, 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. “Our own Earth has aurorae, commonly recognised here as the northern and southern lights. These beautiful aurorae also emit powerful radio waves – this is from the interaction of the planet’s magnetic field with the solar wind,” he said. “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 light from our stars is a scaled-up version of Jupiter and Io, with an exoplanet enveloped in the magnetic field of a star, feeding material into vast currents that similarly power bright aurorae on the star itself.

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

Video explaining aurorae on a star, video was made in 2020 when astronomers first detected aurorae on a star

Future observations with the Square Kilometre Array

The team are now investigating the direct presence of the planets around the star using optical telescopes and searching for periodicity in the radio light. “The radio light should turn on and off like a lighthouse,” Dr Callingham said “and we hope to see that periodicity in new LOFAR data.”

The discoveries with LOFAR are just the beginning, but the telescope only has the capacity to monitor stars that are relatively nearby, up to 165 lightyears away. With the next-generation SKA radio telescopes now under construction in South Africa and Australia and the full arrays expected to be built by the end of 2027, the team predict they will be able to see hundreds of relevant stars out to much greater distances.

This work demonstrates that radio astronomy is on the cusp of revolutionising our understanding of planets outside our Solar System.

Scientific articles

The population of M dwarfs observed at low radio frequencies. J.R. Callingham, H.K. Vedantham, T.W. Shimwell, B.J.S. Pope, I.E. Davis, P.N. Best, M.J. Hardcastle, H.J.A. Röttgering, J. Sabater, C. Tasse, R.J. van Weeren, W.L. Williams, P. Zarka, F. de Gasperin & A. Drabent. Accepted for publication in Nature Astronomy. https://www.nature.com/articles/s41550-021-01483-0

The TESS View of LOFAR Radio-Emitting Stars. Benjamin J.S. Pope, Joseph R. Callingham, Adina D. Feinstein, Maximilian N. Günther, Harish K. Vedantham, Megan Ansdell, & Timothy W. Shimwell. Accepted for publication in Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/ac230c

LOFAR

The International LOFAR Telescope is a trans-European network of radio antennas, with a core located in Exloo in the Netherlands. LOFAR works by combining the signals from nearly 110,000 individual antenna dipoles, located in ‘antenna stations’ across the Netherlands and in partner European countries. The stations are connected by a high-speed fibre optic network, with powerful computers used to process the radio signals in order to simulate a trans-European radio antenna that stretches over 2000 kilometres. The International LOFAR Telescope is unique, given its sensitivity, wide field-of-view, and image resolution or clarity. The LOFAR data archive is the largest astronomical data collection in the world.

LOFAR was designed, built and is presently operated by ASTRON, the Netherlands Institute for Radio Astronomy. France, Germany, Ireland, Italy, Latvia, the Netherlands, Poland, Sweden and the UK are all partner countries in the International LOFAR Telescope.

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