Weblog
23 April 2025
SDO/Morton, et al
In case you occur to be having fun with a sunny day, thank the intense floor of the Solar, referred to as the photosphere. At a piping extreme temperature of about 5,800 Okay, the photosphere offers practically all the daylight Earth receives. However for all its superb radiance, the photosphere isn’t the most well liked a part of the Solar. That award goes to the diffuse outer environment of the Solar referred to as the corona, which has a temperature of greater than one million Kelvin. Components of the corona might be as scorching as 20 million Kelvin, which is hotter than the Solar’s core. In fact, the large thriller is why the corona is so scorching.
For a lot of the Solar, the temperature drops as you progress away from the middle. This is sensible, because it’s nuclear fusion within the core that heats the Solar. So you’ll count on the corona to be cooler than the floor, nevertheless it isn’t. The corona is superheated by some mechanism we haven’t noticed. Till now.
A part of the rationale the corona is so scorching is solely that it’s diffuse. The corona is so diffuse we’d contemplate it a vacuum right here on Earth, and that makes it a lot simpler to warmth than the dense layers of the photosphere. There’s additionally a heating mechanism referred to as magnetic recombination. The equatorial area of the Solar rotates a bit quicker than the polar areas, so the Solar’s magnetic fields get tangled up over time. Finally, the sector strains snap again into alignment, which we name recombination. It’s like snapping a rubber band, and it releases numerous power. However once we add up all of the power we are able to account for by this methodology, it isn’t sufficient to clarify all of the coronal heating. There needs to be one more mechanism.
The preferred candidate is an impact referred to as Alfvén waves. Alfvén waves are low-frequency waves brought on by ions inside a magnetic subject. Because the ions are charged particles, their oscillation additionally creates a magnetic oscillation as a little bit of a suggestions loop. You’ll be able to consider it as a form of background hum, just like that of stereo audio system. The thought is that the Alfvén waves switch fairly a little bit of power to the corona. Earlier calculations have instructed that this would possibly account for the lacking part, however the important thing phrase is would possibly.
This new research makes use of information gathered by the Cryogenic Close to-IR Spectro-Polarimeter (Cryo-NIRSP), which is an instrument on the Inouye Photo voltaic Telescope. The machine makes use of polarization to picture magnetic fields throughout the corona, and from their information, the group captured photographs of Alfvén waves. The pictures affirm the low-frequency waves we’ve recognized about, but in addition present larger frequency waves we didn’t find out about. These larger frequency waves don’t switch practically as a lot power to the corona as low frequency waves, however the truth that they’re current signifies that the Solar’s magnetic fields are effectively transferring power to the corona. This shifts the probability of the Alfvén wave from would possibly to doubtless. It would take extra observations to verify the method, however the truth that we are able to now picture coronal Alfvén waves means we are able to higher perceive how they behave.
So it seems just like the thriller of the corona’s temperature is definitely heating up.
