‘Unprecedented’ view of the sun reveals elusive coronal waves after 85-year search
A burning mystery about the sun may be about to be solved.
For decades, scientists have tried to understand why the sunThe outer atmosphere of the atmosphere is much warmer than its surface, although it is further from the core. While the surface, or photosphere, is millions of degrees Fahrenheit, 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 — the the largest ground-based solar telescope ever built – helps scientists understand how the sun’s energy is transported through its atmosphere.
A solar mystery
Researchers have previously noted the extreme temperature of the solar corona, as well as the supercharged flow of heated gas, called solar wind, that blasts from the sun at more than 1 million mph (1.6 million km/h), said Richard Mortonsolar physicist and professor at Northumbria University in the United Kingdom who led the research, told Live Science in an email.
Both processes require energy, and scientists assumed that rolling convection on the Sun’s surface generated the necessary fuel. But complications emerged during the first studies decades ago.
“We don’t know exactly how [energy] is transferred in the atmosphere and the solar wind, and how the energy is converted into heat and momentum,” Morton said.
In 1942, the Swedish plasma physicist (and future Nobel laureate) Hannes Alfvén suggested that magnetic waves could be responsible. But these waves, now known as Alfvén waves, had until now never been spotted in the corona.
“This was because the sensitivity of previous instruments was not good enough to resolve Alfvén wave motions,” Morton said. “Despite this, many numerical experiments and space weather prediction tools assume that Alfvén waves exist in the corona. However, the properties of the waves they use in the models have been educated guesses.”
“Unprecedented” observations
DKIST has a 4-meter (13-foot) mirror and “unprecedented” resolution of the sun, Morton said, with “much cleaner measurements” (less noise) than any previous solar observatory. In the new research, scientists used the telescope’s cryogenic near-infrared spectropolarimeter (Cryo-NIRSP) to search for Alfvén’s coronal waves.
Cryo-NIRSP can trace the movements of the corona through images, Morton said, as well as examine changes in solar plasma (superheated gas) through a phenomenon known as Doppler shift — the perceived difference in the frequency of a wave as the observer and the source of the wave move closer or further away from each other. (A common, real-world example is the sound of an ambulance’s siren changing when it passes a pedestrian on the street.)
“Cryo-NIRSP provided the data that allowed us to observe the telltale signature of Alfvén waves, which, in a plasma like the corona, is a back-and-forth twist of the magnetic field,” Morton said. “This appears as alternating red and blue Doppler shifts on opposite sides of the magnetic fields. We found that these waves were continually present during the observation period, and given that there was nothing particularly special about the region we observed, this implies that they are probably still common throughout the rest of the atmosphere.”
“Perhaps more importantly,” he continued, “our analysis indicates that the waves are likely carrying a significant amount of energy.”
This is an important discovery, he noted, because astronomers debate between solar waves and magnetic reconnection – when the sun’s magnetic fields twist and break, releasing energy – as the mechanism behind the intense heating of the corona.
While various spacecraft have found evidence that magnetic reconnection is a driver of coronal heating, the new findings from DKIST show that the bigger picture is more complicated. Solar observatories like NASA’s Parker solar probe and the European Space Agency’s Solar Orbiter, along with new data from DKIST, show that “waves and reconnections occur frequently in the Sun’s atmosphere,” Morton said.
“Our research confirms that Alfvén waves are present and carry a significant amount of energy, potentially accounting for at least half of the energy needed to heat the corona,” he added. “However, the exact energy associated with waves is still difficult to estimate.”
The relationship between magnetic reconnection and Alfvén waves affects not only solar heating, but also the light (or more correctly, the radiative power) of the sun, as well as the light of stars beyond our solar system. Scientists hope to use this research to understand how planetary systems have evolved over the long term and to make better short-term predictions about solar wind energy production. “We hope that further studies like the one we published will shed some light on the properties of Alfvén waves to better inform models and improve predictions,” he said.
:max_bytes(150000):strip_icc()/TypesOfBroccoli-6dd837ebc29047889872aeeb175a3646.jpg?w=390&resize=390,220&ssl=1 "What Happens to Your Body When You Eat Broccoli Regularly")
