Scientists have discovered tadpole-like streams emerging from areas subject to intense magnetic fields on the Sun. Unlike those living on Earth, these "tadpoles" – formerly called pseudo-shocks – are made entirely of plasma, the electrically conductive material made up of charged particles that make up about 99% of the observable universe. The discovery adds a new clue to one of the oldest mysteries of astrophysics.
For 150 years, scientists have been trying to understand why the upper atmosphere of the sun, the crown, is more than 200 times warmer than the solar surface. This region, which stretches for millions of kilometers, becomes somewhat overheated and releases permanently charged particles that pass through the solar system at supersonic speeds.
When these particles meet the Earth, they can harm satellites and astronauts, disrupt telecommunications and even interfere with power grids during particularly intense events. Understanding how hot the crown becomes can ultimately help us understand the fundamental physics behind these disturbances.
In recent years, scientists have largely debated two possible explanations for coronal heating: nanoflars and electromagnetic waves. The nanoflare theory proposes bomb – like explosions, which release energy into the solar atmosphere. Brothers and sisters with large solar flares, they are likely to occur when magnetic field lines reconnect explosively, releasing a surge of hot, charged particles. An alternative theory suggests that a type of electromagnetic wave called Alfvén waves could push charged particles into the atmosphere like a sea wave pushing a surfer. Scientists now think that the crown can be heated by a combination of such phenomena rather than just one.
The new discovery of pseudo-shocks adds another player to this debate. In particular, it can bring heat to the crown during specific periods, especially when the sun is active, for example during solar maxima – the most active part of the 11-year cycle of the Sun, characterized by increased staining solar flares, solar eruptions and coronal mass ejections. .
The discovery of solar tadpoles was a bit casual. During a recent analysis of NASA's Imaging Spectrograph data by region of the interface, IRIS, scientists have noticed single elongated jets emerging from sunspots: cold, magnetically active regions on the surface of the Sun, rising to 3,000 km in the inner crown. The jets, with their bulky heads and their rare tails, gave the scientists the taste of tadpoles swimming through the layers of the sun.
"We were looking for waves and plasma ejectas, but instead we have noticed these dynamic pseudo-shocks, like disconnected plasma jets, that do not look like real shocks but are very energetic to offset Sun's radiative losses." said Abhishek Srivastava, scientist at the Indian Institute of Technology (BHU) of Varanasi, India, and lead author of the new paper in Nature Astronomy.
Using computer simulations for the events, they determined that these pseudo-shocks could carry enough energy and plasma to heat the inner ring.
Scientists believe that pseudo-shocks are ejected by magnetic reconnection – an explosive entanglement of magnetic field lines, which often occurs in and around sunspots. The pseudo – shocks have so far been observed only at the sunspot 's edge, but scientists expect them to also find themselves in the dark. other very magnetized regions.
In the last five years, IRIS has kept an eye on the Sun on more than 10,000 orbits around the Earth. This is one of the many NASA fleet vehicles to observe the sun that have been observing the sun continuously over the past two decades. Together, they work to resolve the debate on coronal warming and to solve other mysteries that the Sun keeps.
"Since the beginning, the IRIS scientific investigation has focused on combining high-resolution observations of the solar atmosphere with digital simulations capturing essential physical processes," Bart said. De Pontieu, researcher at Lockheed Martin Solar & Astrophysics Laboratory in Palo Alto, California. "This document is a beautiful illustration of how such a coordinated approach can lead to new physical insights into the factors that determine the dynamics of the solar atmosphere."
Parker Solar Probe, the newest member of NASA's heliophysics fleet, could perhaps provide additional clues to the mystery of coronal warming. Launched in 2018, the spacecraft is flying through the solar corona to track the motions of energy and heat in the region and explore what accelerates the solar wind as well as energetic particles. By examining phenomena well above the region where pseudo-shocks are found, Parker Solar Probe's investigation hopes to highlight other heating mechanisms, such as nanoflares and electromagnetic waves. This work will complement the research conducted with IRIS.
"This new heating mechanism could be compared to the Parker Solar Probe surveys," said Aleida Higginson, assistant project scientist Parker Solar Probe at the Applied Physics Laboratory at Johns Hopkins University, Laurel. Maryland. "Together, they could provide a complete picture of the coronal heating."
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