Radiation bursts are not uncommon on the Sun, but not all of these flares also eject solar plasma into space. Astronomers have now directly observed the reason for such “failed” eruptions for the first time. A magnetic “brake” is responsible for the lack of coronal plasma ejection: a short circuit of magnetic field lines above the rising plasma hinders it and takes away its energy. As a result, the impending outbreak collapses, as the team reports in “Nature”.
Although our sun is a relatively quiet star, it can produce violent bursts of radiation and charged particles. Typically, such a solar storm begins with a series of short circuits between field lines just above the sun’s surface. These magnetic reconnections release energy in the form of radiation, creating the first act of the solar storm – a radiation burst.
The second act of the solar storm begins when the abrupt release of energy mobilizes the solar plasma at the site of the flare. The plasma rises along the curved magnetic field lines. The charged particles are further accelerated until they finally break out of their magnetic cage and are thrown out into space. According to current theory, magnetic reconnections behind the plasma front also provide the necessary thrust.
Why do some plasma eruptions not occur?
The strange thing, however, is that not every strong burst of radiation from the sun also produces a plasma eruption. Sometimes the plasma arcs that have been thrown into the air simply collapse again. “The eruption process is stopped without any material or magnetic structures leaving the sun,” explain Tingyu Gou from the Harvard & Smithsonian Center for Astrophysics in Massachusetts and her colleagues.
But why do some solar flares fail before they even begin? “We have not yet had a comprehensive explanation for such failed outbursts and their mechanisms,” the astronomers write. For a long time there was a lack of observations that showed the processes at the location of a flare, including the magnetic conditions in the solar atmosphere. That has now changed.
Failed escape with witnesses
On March 30, 2024, the time had come: a strong radiation burst occurred on the sun, releasing an intense pulse of high-energy X-rays and UV radiation. At the same time, dense plasma also rose – the beginning of a coronal mass ejection. But the plasma eruption failed. “The flare should have produced a large mass ejection, but it collapsed shortly after it began,” says Gou.
This time there were enough witnesses who were able to follow the entire process of this failed eruption: solar probes such as the Solar Orbiter, the Japanese Hinode probe and several stationary solar observatories and terrestrial telescopes observed the event from multiple angles. They recorded what was happening in the solar magnetic field lines around the flare, but also how the solar plasma behaved during it.
A second short circuit as a brake
The observations revealed: “In addition to the well-known reconnection process below the plasma arc, we also found the clear signature of a second, external reconnection that occurred above it,” the astronomers report. These two magnetic short circuits had very different effects on the incipient plasma eruption: The lower short circuit of the solar magnetic field lines accelerated the charged particles of the rising plasma and opened a window in the solar magnetic cage to the outside.
But the external reconnection above the plasma arc that followed shortly afterwards had the opposite effect: it hit the plasma arc at its apex and weakened the magnetic fields that stabilize and accelerate the solar plasma in this tubular structure. At the same time, this upper reconnection also slowed the rise of further plasma, as Gou and her colleagues report. Overall, this second magnetic short circuit acted like a brake.
New findings also for foreign stars
These observations could explain why not all of the Sun’s strong bursts of radiation also cause coronal plasma ejections. Apparently the decisive factor is whether there are inhibitory magnetic reconnections over the solar flare region. If these are strong enough, they take so much energy from the rising solar plasma that it falls back onto the sun’s surface, as astronomers explain.
At the same time, the new findings provide clues as to why many flares, but only rare plasma ejections, have been observed on foreign stars. “By observing this failed flare on our own sun, we also gain insight into how flares and plasma eruptions work in the rest of our galaxy,” says Gou.
Source: Tingyu Gou (Center for Astrophysics – Harvard & Smithsonian, Cambridge, USA) et al., Nature, 2026; doi: 10.1038/s41550-026-02872-z