Massive stellar explosion reshapes what we know about planetary safety and stability

For years, astronomers talked about coronal mass ejections on other stars almost like ghost stories. You hear signs, hints and clues, but never the thing itself. Our own Sun throws these storms often. They hurl giant clouds of plasma through space, spark auroras and can slowly peel away a planet’s atmosphere. Yet even with decades of searching, no one had caught a confirmed CME from another star in the act.

That mystery has finally cracked open. A team using the LOFAR radio telescope network spotted a short burst of radio light from the nearby red dwarf known as StKM 1-1262. The signal matched the pattern of type II solar radio bursts, which only appear when a fast CME breaks free of a star’s magnetic grip. After years of speculation, you now have the first clear sign that these eruptions are not limited to the Sun.

“Astronomers have wanted to spot a CME on another star for decades,” says Joe Callingham of the Netherlands Institute for Radio Astronomy (ASTRON), author of the new research published in Nature. “Previous findings have inferred that they exist, or hinted at their presence, but haven’t actually confirmed that material has definitively escaped out into space. We’ve now managed to do this for the first time.”

The discovery happened during a sweeping effort to map the northern sky at low radio frequencies. LOFAR’s sensitivity let astronomers track more than 86,000 stars within 100 parsecs for hours at a time. During one of those scans, a two-minute burst drifted from 166 to 120 megahertz. It slid downward in frequency at about minus 0.62 megahertz per second, a trait that closely matches what you see when a shock wave rides ahead of a fast CME.

The burst was bright, reaching an average flux density near 110 millijanskys and spiking around 440 millijanskys. It was also about 90 percent circularly polarized and carried a faint streak of linear polarization. Even more striking were its two parallel lanes of emission, which mirror band-splitting patterns seen in solar type II bursts.

Then it vanished. No other event occurred during the remaining seven hours of watching.

When researchers traced the signal’s origin, it lined up with StKM 1-1262, an active M dwarf spinning once every 1.241 days. This small star sits about 40 parsecs away, glows at roughly 3,916 Kelvin and carries a strong magnetic field near 300 gauss. It is not locked in a binary system and rotates so fast that its equator moves at about 26 kilometers per second.

Using the frequency drift, the team estimated the shock’s speed at nearly 2,400 kilometers per second. On the Sun, only about one CME out of twenty reaches that velocity. Those rare events almost always produce a type II burst.

LOFAR’s giant survey allowed the team to estimate how often M dwarfs might unleash such eruptions. Their calculation suggests a rate near 0.84 times ten to the minus three per day per star. That is low, yet the features match the behavior of fast solar events. The high circular polarization hints that the radio waves came from the fundamental plasma frequency. The faint linear polarization suggests the signal traveled through a relatively clean part of the star’s corona.

That level of clarity is unusual. It may reflect the strong and stable magnetic bubbles that M dwarfs often host.

From the emission frequency, the researchers estimated that the ejected plasma carried an electron density above three hundred million particles per cubic centimeter. That is far higher than many models use when exploring how stellar storms might strike nearby planets.

The burst likely came from a region roughly three stellar radii above the surface. Its brightness temperature reached about one and a half quadrillion Kelvin. Though extreme, plasma emission under the right conditions can reach those levels.

To create a shock, the CME had to outrun the local Alfvén speed. That means the magnetic field in that region had to sit below about 0.05 gauss, implying the eruption traveled beyond the part of the star where magnetic loops can easily hold plasma in place.

Using typical CME masses of about ten to the fifteen grams, the team calculated that this blast would hit a planet at 0.2 astronomical units with a ram pressure near 0.1 dynes per square centimeter. Even a planet with a magnetic field as strong as Earth’s three-gauss shield would struggle to withstand that blow. Its magnetosphere would be pushed down to the surface. Over time, that pressure could strip away much of its atmosphere.

If eruptions like this happen often around stars like StKM 1-1262, any worlds nearby could face relentless space weather strong enough to erode their air.

Until now, astronomers had only indirect hints of CMEs on other stars, such as blueshifted lines or disappearing light in ultraviolet or X-ray wavelengths. These clues were always uncertain because they did not prove that material truly escaped a star’s magnetic cage.

This radio burst changes the picture. A type II burst can only happen when plasma breaks free and heads into interplanetary space. For the first time, you can see a stellar CME as it happens rather than infer it.

The discovery also shows why these eruptions have been so hard to catch. M dwarfs often have magnetic fields thousands of times stronger than the Sun’s. Those fields can trap plasma and stop eruptions from fully escaping. The low rate found here supports the idea that most CMEs on such stars never break out.

Some radio bursts on M dwarfs are caused by a different mechanism known as ECMI. The team tested that idea, but the geometry needed to explain the frequency drift looked unrealistic. ECMI events also tend to repeat with each rotation, and no follow-up observations showed a second burst. That leaves a type II burst as the most convincing answer.

This finding opens a new path for studying how stellar storms rise, escape and race through space. It carries major consequences for worlds around small stars. Their habitable zones lie close to the star, which means any planet in those orbits could meet fast, dense CMEs far more often than Earth does.

As surveys continue, LOFAR may find more of these rare events. The upcoming Square Kilometre Array could reveal many more, giving you a clearer picture of how space weather behaves on the stars that host most of the Milky Way’s planets.

“This work opens up a new observational frontier for studying and understanding eruptions and space weather around other stars,” adds Henrik Eklund, an ESA research fellow based at the European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands.

“We’re no longer limited to extrapolating our understanding of the Sun's CMEs to other stars. It seems that intense space weather may be even more extreme around smaller stars – the primary hosts of potentially habitable exoplanets. This has important implications for how these planets keep hold of their atmospheres and possibly remain habitable over time.”

This work reshapes how you understand the safety and stability of planets around red dwarfs. These eruptions can tear away atmospheres, which threatens the long-term survival of air and water on worlds that might otherwise stay warm enough for life.

With confirmed evidence that CMEs escape from such stars, scientists can now build more accurate models of habitability and space weather.

This will guide future searches for life, shape telescope mission planning and help explain how planets across the galaxy evolve under harsh stellar storms.

Research findings are available online in the journal Nature.

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