Particle accelerator region revealed inside solar flare

Solar flares are among the most violent outbursts in our solar system, but despite their immense energy – equivalent to a hundred billion atomic bombs exploding at once – physicists have still not been able to answer exactly the nature of these sudden eruptions on the Sun. capable of launching particles to Earth, nearly 93 million kilometers away, in less than an hour.

However, in a study published on June 8 in Nature, Researchers from the New Jersey Institute of Technology (NJIT) have identified the precise location where charged particles from solar flares are accelerated to near the speed of light.

The new findings, made possible by observations of an X-class solar flare in 2017 by NJIT’s Owens Valley Solar Array (EOVSA) Expanded Radio Telescope, have revealed a highly efficient particle accelerator located at the tip of the highest point glowing from the flare in the Sun’s outer atmosphere, called the flare’s “cusp region”, where ambient plasma from the flare is converted into high-energy electrons.

The researchers say the discovery of the region, measured at almost twice the volume of Earth, could open new doors for studying fundamental particle acceleration processes ubiquitous in the universe.

“The results of this study help explain the long-standing mystery of how solar flares can produce so much energy in just seconds,” said Gregory Fleishman, corresponding author of the paper and distinguished research professor in physics at the NJIT Solar-Terrestrial Research Center. . “The flare unleashes its power in a much larger region of the Sun than predicted by the classic model of solar flares. Although others have postulated that this must happen, this is the first time that the size, shape and location of this key region were identified, and the efficiency of energy conversion into particle acceleration inside the flare was measured.”

The finding follows separate 2020 studies published in Science and natural astronomywhere EOVSA’s detailed snapshots of the eruption and changes in the Sun’s magnetic field – taken at hundreds of radio frequencies at once – initially gave the NJIT team a lead on the location.

“Our recent studies suggested that the flare cusp could be where such high-energy electrons are produced, but we weren’t sure,” said Bin Chen, associate professor at NJIT and co-author. author of the article. “We initially discovered a bottle-shaped magnetic structure at the site that contained an extremely high number of electrons compared to anywhere else in the flare, but now with the new measurements from this study, we can say with more confidence that it is the particle of the eruption accelerator.”

Using EOVSA’s unique microwave imaging capabilities, the team was able to measure the electron energy spectrum at hundreds of locations of an X-class solar flare triggered by a reconfiguration of magnetic field lines on along the surface of the Sun on September 10, 2017.

“The EOVSA spectral imagery gave us a full thermal plasma map of the eruption as it evolved second by second. But to our surprise, what we found was a mysterious hole in the eruption. the thermal plasma map that began to develop at the tip of the eruption,” said Gelu Nita, NJIT research professor and co-author of the paper. “More than that, as the thermal particles in the region disappeared, the hole was then densely filled with high-energy non-thermal particles.”

The team’s analysis shed light on an incredibly efficient energy conversion process in the solar flare’s particle accelerator, where intense energy from the Sun’s magnetic fields is quickly released and transferred into kinetic energy. inside the region.

“We wondered how efficient this energy conversion process would be… how many particles in this area would be accelerated beyond the thermal energy of the explosion?” added Sijie Yu, study co-author and assistant research professor at NJIT. “Using extreme ultraviolet data from the Sun, we confirmed that there were virtually no particles left inside the region at thermal energies below a few million Kelvin, consistent with the EOVSA measurement that the particles all had been accelerated to non-thermal energies greater than 20 keV, or nearly 100 million Kelvin.”

The team now says these latest findings could help scientists investigate fundamental questions in particle physics that aren’t possible on Earth, as well as offer new insights into how these high-energy particles from the Sun might impact Earth in future space weather events.

“An important aspect of this study is that it draws theorists’ attention to precisely where most of the energy release and particle acceleration occurs, and provides quantitative measurements to guide numerical models,” says Dale Gary, NJIT professor emeritus and director of EOVSA. “However, to extend our measurements to much wider flare regions and to weaker but more frequent flare events, we are developing a dedicated next-generation solar power radio network called the Frequency-Agile Solar Radio Telescope. , which will be at least 10 times larger and commands of a more powerful magnitude.”

“We still want to investigate the physical mechanism behind the acceleration of particles in solar flares. But future studies must take into account what we now know about these huge explosions – both the primary energy release in the cusp region and the 100% efficiency at which charged particles acceleration occurs,” Fleishman said. “These results call for a major revision of the models we use to study solar flares and their impact on Earth. .”

This research was supported by grants from the National Science Foundation.


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