“It’s the first time we have detected one,” says Cyril Tasse of the Paris Observatory, referring to a coronal mass ejection, or CME, erupting from any star other than the Sun. Caught in unprecedented detail, the event was no ordinary stellar hiccup but at least 10,000 times more violent than even the most powerful solar storms recorded on Earth, and it could have obliterated the atmosphere of any nearby planet.
The discovery centered on StKM 1-1262, a red dwarf star more than 133 light-years away. Red dwarfs-M dwarfs-are small and cool compared to the Sun, possessing only 10 to 50 percent as much mass as our star. But they are anything but serene. Their intense magnetic activity can generate CMEs with enormous energies, powered by releases known as magnetic reconnection events in their coronae. In this case, the researchers clocked the CME at nearly 2,400 kilometers per second a velocity matched by only about 5 percent of solar CMEs dense and fast enough, they say, to strip the atmosphere from any planet in close orbit to its star.
The detection was made possible by the Low Frequency Array, or LOFAR, the most sensitive low-frequency radio telescope network ever built. LOFAR’s antennas, spread across eight European countries, continuously monitor wide swaths of the sky. Although the array is often tuned to study phenomena such as black holes, its wide field of view means stars are always in the background. In 2016, a one-minute burst from StKM 1-1262 was recorded as a “type II radio burst,” a signature produced when a CME’s shock wave propagates through a star’s outer atmosphere into interplanetary space. This was the first definitive radio confirmation of a CME beyond the Sun.
Confirmation of the event’s true nature required more than radio data. The ESA’s XMM-Newton X-ray observatory measured the star’s temperature, its rotation, and its high-energy emission, showing that StKM 1-1262 rotates about 20 times faster than the Sun and boasts a magnetic field roughly 300 times more intense. Such extreme magnetic conditions are responsible for driving the violent, erratic behavior of many M dwarfs.
Stellar magnetism forms the basis of the physics of these eruptions. In red dwarfs, particularly those of mid- to late-spectral type, fully convective interiors replace the Sun’s layered structure, removing the tachocline but still generating powerful magnetic fields via turbulent dynamos. These fields may become twisted and unstable, releasing their stored energy in explosive CMEs. The LOFAR detection also agrees with a statistical result stating that radio efficiency increases with spectral type among active stars-meaning that later-type M dwarfs are more likely to generate detectable radio bursts from such events.
The implications, from a planetary habitability point of view, are sobering. Red dwarfs represent prime targets in the search for Earth-sized exoplanets, both because their small size makes their planets relatively easy to detect when they transit, and because their habitable zones lie close to the star. But proximity is also a double-edged sword: planets residing in these zones are far more exposed to stellar space weather. In the words of Joe Callingham of the Netherlands Institute for Radio Astronomy, These CMEs happen so regularly, and they’re hitting the planets so regularly, that they strip the atmosphere. So, great you’re in the Goldilocks zone, but you’ve got no help here.
Such questions are now being addressed through the emergent field of “exospace weather.” The UV-optimized small satellite SPARCS will provide flare and CME monitoring on low-mass stars. Next-generation radio facilities, including the Square Kilometre Array, are predicted to detect “tens to hundreds” of extrasolar CMEs per year, which will enable the frequency and severity of atmospheric-stripping events to be mapped out across different stellar types.
The StKM 1-1262 CME marks a turning point: for the first time, scientists have directly observed the kind of stellar storm that could dictate whether a planet retains its air or becomes a barren rock. It confirms that the violent processes shaping our own solar environment are active across the galaxy sometimes in far more extreme forms.
