The solar corona, or atmosphere, imaged during a total eclipse on 2 July 2019. (ESA/CESAR)
Neutrinos, the tricky little particles that just stream through the Universe like it's virtually nothing, may actually interact with light after all.
According to new calculations, interactions between neutrinos and photons can take place in powerful magnetic fields that can be found in the plasma wrapped around stars.
It's a discovery that could help us understand why the Sun's atmosphere is so much hotter than its surface, say Hokkaido University physicist Kenzo Ishikawa and Yutaka Tobita, a physicist from Hokkaido University of Science – and, of course, to study the mysterious ghost particle in greater detail.
"Our results are important for understanding the quantum mechanical interactions of some of the most fundamental particles of matter," Ishikawa says. "They may also help reveal details of currently poorly understood phenomena in the Sun and other stars."
Neutrinos are among the most abundant particles in the Universe, second only to photons. But they keep to themselves, mostly. Neutrinos are almost without mass, and barely interact with matter. To a neutrino, the Universe is as nothing – shadows or specters, through which they pass with ease. Billions of neutrinos are passing through you right now, like teeny tiny ghosts.
But scientists believe neutrinos could be important for probing astrophysical phenomena, and figuring out why the Universe is the way it is, and refining our understanding of particle physics. Working out if, and how, they interact with the Universe not only reveals information about neutrinos, but about particle interactions, and the quantum Universe.
The work of Ishikawa and Tobita is theoretical, using mathematical analysis to determine the circumstances under which neutrinos can interact with electromagnetic quanta – photons. And they discovered that highly magnetized plasma – gas that is either positively or negatively charged, due to the subtraction or addition of electrons – offers the right environment.
"Under normal 'classical' conditions, neutrinos will not interact with photons," Ishikawa says.
"We have revealed, however, how neutrinos and photons can be induced to interact in the uniform magnetic fields of the extremely large scale – as large as 103 km – found in the form of matter known as plasma, which occurs around stars."
Previously, Ishikawa and Tobita explored the possibility that a theoretical phenomenon known as the electroweak Hall effect could facilitate neutrino interactions in the solar atmosphere. This is when, under extreme conditions, two of the Universe's fundamental interactions, electromagnetism and the weak force, sort of smoosh together into one.
Under electroweak theory, neutrinos could interact with photons, the researchers found. If a star's atmosphere could produce the right kind of environment for the electroweak Hall effect, these interactions could be taking place there.
In their paper, Ishikawa and Tobita calculate the energy states of the system of the photon and neutrino during this interaction.
"In addition to its contribution to our understanding of fundamental physics, our work might also help explain something called the solar corona heating puzzle," Ishikawa says.
"This is a long-standing mystery concerning the mechanism by which the outermost atmosphere of the Sun – its corona – is at a much higher temperature than the sun's surface. Our work shows that the interaction between neutrinos and photons liberates energy that heats up the solar corona."
In future work, the duo hope to further investigate how neutrinos and photons exchange energy in extreme environments.
The research has been published in Physics Open.
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