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Danielle Futselaar

Auroras on nineteen stars hint at hidden exoplanets

An international team of scientists including Leiden's Joe Callingham has discovered nineteen red dwarf stars that unexpectedly emit radio waves. The outbursts possibly originate from interaction with exoplanets. The results of the research appear in two scientific publications.

The scientists searched for auroras around red dwarf stars with the help of LOFAR. This is the most powerful radio telescope in the world with its centre in Exloo, The Netherlands. A year ago, the same team was the first to discover auroras around a star and that made them long for more.

Signal reveals hidden planets

The researchers have now picked up similar signals from 19 red dwarf stars. In the case of four stars, the signals could best be explained by the fact that they would be interacting with exoplanets that orbit them. However, the exoplanets themselves have not yet been found.

Explanation: How auroras can expose an exoplanet

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Collision with solar wind creates auroras

Astronomers have long known that planets, like our Earth, emit powerful radio waves when their magnetic field collides with the solar wind. Callingham: 'With our Earth, this results in the Northern light and the Southern light. And for Jupiter the aurora is even more intense because the volcanic moon Io blows lots of fast-moving particles (or: plasma) towards Jupiter.'

The researchers' models show that something similar to Jupiter's aurora could be going on with the investigated stars. Co-author Harish Vedantham (ASTRON): 'The aurora on the star is then caused by an exoplanet near the star that blows a lot of plasma into space.’

Red dwarf star with aurora. An artistic rendering of a red dwarf star's aurora (left) due to interaction with an exoplanet (right). Credits: Daniëlle Futselaar (artsource.nl)

The search can begin

The team is now subjecting the nineteen stars to further investigation. They are using optical telescopes to search for clues about exoplanets and looking in the radio waves for suspicious patterns. In the future, the researchers want to use the SKA telescopes for this. This Square Kilometre Array is a large radio telescope, consisting of thousands of receivers, which is currently being built in South Africa and Australia. The telescopes have to be ready in 2029.


The population of M dwarfs observed at low radio frequencies. Door: 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. Nature Astronomy. https://www.nature.com/articles/s41550-021-01483-0

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

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