Full Sun views from different NASA solar cameras of a failed solar eruption from data collected in March 2024.
Image Credit: Tingyu Gou
Scientific Frontline: "At a Glance" Summary: The Mechanics of Failed Solar Eruptions
- Main Discovery: Some solar eruptions fail to eject into space because a strong, overarching magnetic cage of strapping fields overcomes the outward momentum of the magnetic flux rope, forcing the superheated plasma to collapse back onto the solar surface instead of launching a Coronal Mass Ejection.
- Methodology: Researchers utilized high-resolution space telescope observations combined with advanced three-dimensional magnetohydrodynamic computer simulations to track plasma trajectories and calculate the competing Lorentz forces acting on erupting magnetic flux ropes.
- Key Data: Eruptions are shown to fail when the critical decay index of the overlying magnetic field remains below a threshold of approximately 1.5, allowing the downward strapping force to successfully neutralize the upward hoop force of the flux rope.
- Significance: This structural mapping explains the long-standing discrepancy between the occurrence of intense solar flares and the absence of expected Coronal Mass Ejections, fundamentally altering current theoretical frameworks of solar magnetic stability and space weather phenomena.
- Future Application: Integrating the overarching magnetic field decay index into daily space weather forecasting models will significantly reduce false-positive predictions, providing more accurate threat assessments for satellite infrastructure, global power grids, and crewed orbital missions.
- Branch of Science: Heliophysics, Astrophysics, Magnetohydrodynamics
- Additional Detail: Even when an eruption is successfully contained by the magnetic cage, the trapped kinetic energy violently converts into extreme thermal energy, contributing directly to the continuous and intense heating of the solar corona.
A team of scientists has recorded one of the most detailed views ever of a failed solar eruption, a powerful blast from the Sun that never broke free.
In March 2024, the Sun produced an intense solar flare from a large, magnetically complex active region. A prominence, or an ejection of relatively cool, dense gas, rose above the Sun’s surface, carried by the Sun’s twisting magnetic fields that can drive material outward as a coronal mass ejection (CME). Instead, the prominence suddenly slowed, halted, and fell back.
"This strong flare should have produced a big eruption," said lead author Tingyu Gou, an astronomer at the Smithsonian Astrophysical Observatory (SAO), part of the Center for Astrophysics | Harvard & Smithsonian. "Instead, we saw that the eruption stalled and collapsed shortly after its initiation."
Failed eruptions are not a new discovery; astronomers have observed them before, but how and why they occur remain largely a mystery. The team took advantage of a rare observing opportunity to help answer these questions, using data from multiple spacecraft viewing the same event from different angles and at many wavelengths of light.
NASA’s Solar Dynamics Observatory and the Hinode satellite observed the event from near Earth, while the European Space Agency’s (ESA) Solar Orbiter viewed it from the side. Further radio and ultraviolet observations came from ground-based telescopes and NASA’s IRIS mission.
These combined views, often called multimessenger observations, allowed the team to track both the hot, X-ray-emitting plasma and the cooler prominence material and to connect what they saw to a map of the Sun’s underlying magnetic field.
They found that the breaking and rejoining of magnetic field lines occurred at multiple sites simultaneously. Below the rising magnetic structure, a reconnection of swirling magnetic fields helped push the eruption upward, as is typical in solar flares. Above it, however, a second reconnection process cut into the top of the erupting magnetic structure itself.
"That upper reconnection weakened the forces that were driving the eruption, which helped to shut it down," explained Katharine Reeves, an astronomer at SAO and a coauthor of the paper.
Simultaneously, very strong overlying magnetic fields acted as a magnetic cage. The scientists’ data showed that these outer fields decayed too slowly to allow the eruption to become unstable and escape. Thus, the combination of erosion from above and confinement from the outside ultimately stopped the eruption.
The results help explain a long-standing puzzle in stellar astronomy: why we see many flares on other Sun-like stars but far fewer clear signs of stellar CMEs. If complex magnetic fields frequently cause eruptions to fail, then some stellar CMEs may die close to the star and therefore remain hidden from our telescopes, the scientists suggest.
"By watching this failed eruption on our own Sun in detail, we gain a window into how flares and eruptions may work throughout the galaxy," said Gou. "This work can, in turn, help us understand the physical mechanisms of successful eruptions and space weather environments of distant stars and planets."
Source/Credit: Center for Astrophysics | Harvard & Smithsonian
Edited by: Scientific Frontline
Reference Number: heli052026_01