More stars than ever before have been observed ejecting huge bursts of electrically charged particles into space. Learning more about the behaviour will be important for understanding whether planets orbiting the stars are potentially habitable or not.

Stars like our sun are known to produce coronal mass ejections, huge eruptions of electrically charged particles from the outer atmosphere caused by instabilities in the star’s magnetic field. They are often associated with solar flares, flashes of light resulting from the explosive realignment of twisted magnetic fields.

While we have been able to observe flares on other sun-like stars with relative ease, coronal mass ejections have been more difficult to spot as they are hidden by the glare of the star. But now Astrid Veronig at the University of Graz in Austria and her colleagues have used a new method to spot 21 such ejections. “This is more detections than have been [found in] all previous studies,” says Veronig.

The researchers used historical data from three space-based telescopes to study the ultraviolet and X-ray emissions of more than 200 stars. These high-energy emissions only come from a star’s hot outer atmosphere, called the corona, where temperatures reach millions of degrees.

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In 13 stars, most of which were like our sun, the researchers saw dips in these emissions lasting up to 10 hours, with 21 such events spotted. They argue that these dips are the result of coronal mass ejections throwing material from the star into space, reducing the mass of the corona.

In some instances, the ejections were huge. “The strongest events saw a decrease [in UV and X-ray emissions] by 50 per cent,” says Veronig. In each case, it is thought that the corona then recovered its mass in a matter of hours or days, based on studies of our sun.

It is hoped that this method could be used to identify coronal mass ejections from more stars in future. Doing so could give us vital information about the activity of other sun-like stars, with potential implications for the habitability of any planets orbiting them.

If a star releases a very strong coronal mass ejection and a planet in the firing line is close enough, “you can drive away the whole atmosphere from the planet”, says Veronig.

Journal reference: Nature Astronomy, DOI: 10.1038/s41550-021-01345-9