“Sometimes you only need one of these big guys to come your way,” observed Julián Alvarado-Gómez of the Leibniz Institute for Astrophysics Potsdam. These comments evoke the significance of the recent milestone that has pushed the boundaries of space weather research forward by a considerable margin, namely the first detection of a coronal mass ejection from another star beyond our own Sun.
The offending object is StKM 1-1262, a cool and small M-dwarf star only 130 light-years from us. Although small, with about half the mass of our own Sun, its magnetic field is 300 times stronger than our own. Observing with the Low Frequency Array (LOFAR), which consists of over 20,000 antennas across Europe, they spotted a short and powerful type II radio burst. Such events are the telltale sign of a shock wave generated by a CME crashing through a star’s corona. The phenomenon has long been known from observations of our own Sun, but never detected in stellar observation before. The low-frequency sensitivity of LOFAR made it possible to monitor the motion of this shock wave, while data obtained with XMM-Newton from the space agency ESA provided vital data on the object’s X-ray characteristics.
The speed of this CME 2400 km/s makes it one of the fastest out of every 2000 solar CMEs. At that speed, it would compress a planétè’s magnetósphere to its surface, leaving it vulnerable to bacterially sterilizing particle flows. The brightness of this event was 100 times more brilliant than all previous solar CMEs combined and came close to the 1859 Carrington Event that affected telegraph lines and caused aurorae near the equator. Planètes that find themselves within the close “Goldilocks zone” of M dwarfs frequently no more than 0.1 AU from their star could have atmosphères stripped away within minutes.
The observation employed indirect signatures of CMEs, which is necessary due to difficulties in obtaining imagery of distant star coronas. Type II radio bursts result from shocks produced by CMEs, which excite Langmuir waves, leading to radio waves, and the frequency drift rate of these bursts measures shock velocity in plasma, and/or coronal dimming in extreme ultraviolet lines to determine mass and velocity of CMEs. Future missions, like ESCAPE, which possess an effective area of up to 100 cm² and have a resolution of sub-2 Å, propose to enable routine observation of this process to allow statistical analysis of its occurrence in different types of stars.
The implications of such findings regarding the habitability of exoplanets are quite daunting. Studies by Chuanfei Dong at Princeton Plasma Physics Laboratory indicate that the effect of both stellar wind and CMEs can cause the erosion of planetary atmospheres on a timescale of millions of years, particularly for tidally locked planets whose habitable side is perpetually facing the star. M-dwarf stars may live for a longer period, but they are magnetically active for billions of years, and hence they passionately spew massive flares and CMEs.
This is attested by the analogs from the past. Young sun-like stars similar to EK Draconis have been seen expelling multi-temp CMEs at the rate of several hundred km/s, enough for stellar planetary atmospheres to be altered. It was these same kind of storms that may have contributed to the depletion of atmospheres on Mars and Venus and the possible making of the Earth as a habitable planet when the solar system was still young. StKM 1-1262 would have CMEs with a recurrence interval that is estimated at 500 years. The technology used in LOFAR and XMM-Newton was crucial.
The separated dipole array of LOFAR is very sensitive to decameter to hecmeter wavelengths. This is ideal for type II bursts from distant stars. The X-ray spectrometers and imaging qualities of XMM-Newton enable accurate measurement of temperatures and densities of coronas. These values are necessary for checking radio burst observations. Both helped to overcome observational difficulties for decades to provide the first definitive proof that stellar CMEs are not exclusive to our sun.
Future facilities like the Square Kilometre Array (SKA) promise to extend these capabilities, potentially detecting tens to hundreds of stellar CMEs annually and mapping the statistical landscape of stellar space weather. As ESA’s Henrik Eklund noted, “We’re no longer limited to extrapolating our understanding of the Sun’s CMEs to other stars.” For the search for habitable worlds, this means confronting a new variable: whether a planet’s magnetic shield can withstand the fury of its star long enough for life to take hold.
