Researchers, including those from the Indian Institute of Astrophysics: Bangalore and the Indian Institute of Technology (BHU) Varanasi, have observed a magnetic explosion on the scorching upper reaches of the Sun's atmosphere -- the likes of which have never been seen before.
Using NASA's Solar Dynamics Observatory, the researchers found a prominence -- a large loop of material launched by an eruption on the solar surface -- which started falling back to the surface of the Sun.
However, their study published in the Astrophysical Journal, noted that before the loop could make it, the prominence ran into a snarl of magnetic field lines, sparking an explosion.
The researchers said the observation confirms a decade-old theory, and may help scientists understand a key mystery about the Sun's atmosphere.
"This was the first observation of an external driver of magnetic reconnection," said study co-author Abhishek Srivastava, a solar scientist at Indian Institute of Technology (BHU), in Varanasi.
According to the scientists, the findings may help better predict space weather, and may also lead to breakthroughs in the controlled fusion and lab plasma experiments.
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"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," Srivastava said.
The study noted that this new explosion-driven type called forced reconnection had never been seen directly, thought it was first theorized 15 years ago.
It said spontaneous reconnection happened in regions on the Sun with just the right conditions such as having a thin sheet of ionized gas, or plasma, that only weakly conducts electric current.
But based on the new findings, the researchers said, the new type -- forced reconnection -- can happen in a wider range of places, such as in plasma that has even lower resistance to conducting an electric current.
However, the study said, it can only occur if there is some type of eruption to trigger it which can squeeze the plasma and magnetic fields, causing them to reconnect.
While the Sun's magnetic field lines are invisible, they have an effect on the soup of ultra-hot charged particles known as plasma surrounding it.
With this observation, the scientists could directly see the forced reconnection event for the first time in the Sun's uppermost atmospheric layer, the corona.
The researchers said a prominence in the corona could be seen falling back into the sun's atmosphere in a series of images taken over an hour.
En route, they said, the prominence ran into a snarl of magnetic field lines, causing them to reconnect in a distinct X shape.
According to the study, the new observation offers one explanation for how the corona is millions of degrees hotter than lower atmospheric layers -- a mystery that has led solar scientists for decades to search for what mechanism is driving that heat.
When the scientists observed multiple ultraviolet radiation stemming from the solar event, they could estimate the temperature of the plasma during and following the reconnection event.
Their calculations showed that the prominence, which was fairly cool relative to the blistering corona, gained heat after the event.
Based on these estimates, the researchers suggested that forced reconnection might be one way the corona is heated locally.
They said while spontaneous reconnection can also heat plasma, forced reconnection seemed to be a much more effective heater -- raising the temperature of the plasma quicker, higher, and in a more controlled manner.
The study added that while a prominence was the driver behind the reconnection event in the current study, other solar eruptions like flares and coronal mass ejections, could also cause forced reconnection.
It said the bursts of solar radiation can damage satellites around Earth, and added that understanding the forced reconnection phenomenon can help space weather modelers better predict when disruptive high-energy charged particles might come speeding at Earth.
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