AOP researchers have used data from a NASA space mission to shed light on one of the most violent phenomena in our solar system – magnetic explosions on the surface of the Sun.
Abhishek Srivastava, formerly a research associate at AOP and now a solar scientist at the Indian Institute of Technology (BHU) in Varanasi, India and AOP’s Professor Gerry Doyle have used NASA’s Earth-orbiting Solar Dynamics Observatory satellite to observe a solar explosion, the likes of which have never been seen before. In the scorching upper reaches of the Sun’s atmosphere, a prominence — a large loop of material launched by an eruption on the solar surface — started falling back to the surface of the Sun. But before it could make it, the prominence ran into a snarl of magnetic field lines, sparking a magnetic explosion.
Scientists have previously seen the explosive snap and realignment of tangled magnetic field lines on the Sun — a process known as magnetic reconnection — but never one that had been triggered by a nearby eruption. The observation, which confirms a theory put forward a decade ago, may help scientists understand a key mystery about the Sun’s atmosphere, better predict space weather, and may also lead to breakthroughs in the controlled fusion and lab plasma experiments.
“This was the first observation of an externally-triggered magnetic reconnection,” said Srivastava. “This could be very useful for understanding other systems. For example, Earth’s and planetary magnetospheres, other magnetized plasma sources, including experiments at laboratory scales where plasma is highly diffusive and very hard to control.”
Previously a type of magnetic reconnection known as spontaneous reconnection has been seen, both on the Sun and around Earth. But this new explosion-driven type — called forced reconnection — had never been seen directly, thought it was first theorised 15 years ago. The new observations, which have just been published in the peer-reviewed Astrophysical Journal, allowed Shrivastava and Doyle to directly see the forced reconnection event for the first time in the solar corona — the Sun’s uppermost atmospheric layer. In a series of images taken over an hour (see links at end of post), a prominence in the corona could be seen falling back into the photosphere. En route, the prominence ran into a snarl of magnetic field lines, causing them to reconnect in a distinct X shape.
Since these eruptions drive space weather — the bursts of solar radiation that can damage satellites around Earth — understanding forced reconnection will help scientists better predict when disruptive high-energy charged particles might come speeding at Earth. Understanding how magnetic reconnection can be forced in a controlled way may also help plasma physicists reproduce reconnection in the lab in the quest to achieve practical nuclear fusion.
Scientists are continuing to look for more forced reconnection events. With more observations, they can begin to understand the mechanics behind the reconnection and how often it might happen. Hopefully, the new discovery will help solve the decades-old coronal heating problem, in other words why the solar corona, at several million degrees Kelvin, is a thousand times hotter than the underlying layer, the photosphere. “Our thought is that forced reconnection is everywhere,” Srivastava said. “But we have to continue to observe it, to quantify it, if we want to prove that.”