Stellar eruptions in the laboratory: First experimental evidence for their suppression in strong magnetic fields

An international team of astrophysicists and plasma physicists has achieved the first experimental confirmation that strong magnetic fields can entirely suppress coronal mass ejections (CMEs), offering new insights into why such eruptions are rare on stars beyond the Sun. The breakthrough, detailed in a study published in Physical Review Letters, was made using laboratory experiments that recreated stellar eruptions under controlled conditions. The experiments were conducted at the Ecole Polytechnique in France, where researchers used high-energy lasers to generate plasma flows mimicking the core of solar CMEs. By applying varying levels of magnetic fields, the team observed how these fields influenced the behavior of the plasma. Under weaker magnetic fields, the plasma expanded and moved outward as expected. But with stronger magnetic fields, the flow became unstable, fragmented, and eventually stopped. This demonstrated that intense magnetic fields could act as a barrier, preventing CMEs from escaping into space. Julián D. Alvarado-Gomez, a senior scientist at the Leibniz Institute for Astrophysics Potsdam, played a key role in connecting the laboratory findings to real-world stellar environments. He explained that the combination of theoretical models, experimental data, and numerical simulations allowed the team to validate a longstanding hypothesis, that magnetic fields on active stars might prevent CMEs from occurring or escaping. Julien Fuchs, who led the experimental work, noted that the results were unexpected yet crucial. “When we increased the magnetic field strength and saw the change in behavior of the propagating plasma, it was a clear sign that something fundamental was happening,” he said. The experiments revealed that the interaction between the expanding plasma and the magnetic field could lead to a phenomenon known as kink instability, where the flow bends and reverses direction. The kink instability occurs when the external magnetic field becomes strong enough to exert a dominant force on the plasma. This causes the flow to lose its forward motion and either collapse back onto itself or remain confined within the magnetic structure. The discovery suggests that many CMEs on active stars may not reach space at all, being instead trapped by the surrounding magnetic field. This would explain why such eruptions are rarely observed on stars other than the Sun. The implications extend beyond understanding stellar activity. The study highlights the potential impact of magnetic suppression on exoplanets. CMEs are among the most energetic phenomena in space, capable of stripping planetary atmospheres or altering their chemical composition. If many CMEs are prevented from escaping due to strong magnetic fields, some exoplanets may experience a more stable and less hostile space environment. This could improve their chances of maintaining atmospheres over geological timescales, potentially enhancing their habitability. The research marks a significant step in bridging laboratory physics with astrophysical observations. By replicating stellar processes in a controlled setting, scientists have gained valuable insight into mechanisms that shape the behavior of stars and their planetary systems. Future studies will likely focus on refining the models and exploring how variations in magnetic field strength affect different types of stellar eruptions.