The hot mystery of the Sun may be close to being solved.
For decades, scientists have tried to understand why SunThe planet's outer atmosphere is much hotter than its surface, despite being further away from the core. While the temperature of the surface, or photosphere, is millions of degrees Fahrenheit, the temperature of the outer atmosphere is only about 10,000 F (5,500 C).
New data from the National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) in Hawaii. largest ground-based solar telescope ever built — helps scientists learn how solar energy is transmitted through the atmosphere.
Solar mystery
Previously, researchers had noted the extreme temperatures of the solar corona, as well as a supercharged stream of heated gas called the solar wind, which emanates from the Sun at speeds of more than 1 million miles per hour (1.6 million km/h). Richard Mortonsolar physicist and professor at Northumbria University in the UK, who led the study, told Live Science via email.
Both processes require energy, and scientists have suggested that convection on the surface of the Sun generates the necessary fuel. But complications arose during the first studies this decade ago.
“It’s not clear how this [energy] transferred into the atmosphere and the solar wind, and how the energy is converted into heat and momentum,” Morton said.
In 1942, a Swedish plasma physicist (and possible Nobel laureate) Hannes Alfvén suggested that magnetic waves might be responsible. But these waves, now known as Alfvén waves, have never been observed in the corona until now.
“This happened because the sensitivity of previous instruments was not good enough to resolve the motion of Alfven waves,” Morton said. “Despite this, many numerical experiments and space weather forecasting tools suggest that Alfven waves exist in the corona. However, the wave properties they use in their models are educated guesses.”
'Unprecedented' sightings
DKIST has a 4-meter (13-foot) mirror and “unprecedented” resolution of the Sun, with much “cleaner measurements” (less noise) than any previous solar observatory, Morton said. In the new study, scientists used the telescope's Cryogenic Near-Infrared Spectropolarimeter (Cryo-NIRSP) to search for coronal Alfven waves.
According to Morton, Cryo-NIRSP can image the motion of the corona and also probe changes in the solar plasma (superheated gas) through a phenomenon known as Doppler shift—the perceived difference in wave frequency when the observer and the source of the wave move toward or away from each other. (A common real-life example is the sound of an ambulance siren changing when it passes a pedestrian on the street.)
“Cryo-NIRSP provided data that allowed us to observe the characteristic signature of Alfvén waves, which in plasmas such as the corona represent a two-way twisting magnetic field“It looks like an alternating pattern of red and blue Doppler shifts on opposite sides of the magnetic fields. We found that these waves were constantly present during the observations, and given that there was nothing special in the region we observed, this means that they are probably always common in the rest of the atmosphere.”
“Perhaps most importantly,” he continued, “our analysis shows that the waves are likely carrying significant amounts of energy.”
This is an important discovery, he noted, because astronomers are debating between solar waves and magnetic reconnection — when magnetic fields on the Sun twist and snap, releasing energy — like the intense heating mechanism in the corona.
Although various spacecraft have found evidence that magnetic reconnection is the driving force behind the heating of the corona, the new DKIST results show that the full picture is more complex. Solar observatories such as NASA's Parker Solar Probe and the European Space Agency's Solar Orbiter, as well as recent data from DKIST, show that “both waves and reconnection occur frequently in the solar atmosphere,” Morton said.
“Our study confirms that Alfven waves are present and carry significant amounts of energy, potentially at least half the energy needed to heat the corona,” he added. “However, the exact energy associated with the waves is still difficult to estimate.”
The relationship of magnetic reconnection to Alfvén waves affects not only solar heating, but also the light (or more accurately, the radiation output) of the Sun, as well as the light of stars beyond our planet. solar system. Scientists hope to use this research to understand how planetary systems have evolved over the long term and make more accurate short-term predictions about solar wind production. “It is hoped that further studies like the one we have published will shed some light on the properties of Alfven waves, allowing models to be better informed and predictions to be improved,” he said.
