We have seen the beautiful images and videos of the loops. They are curved magnetic forms that cause bright glowing plasma to travel along their path. They arch above the Sun, sometimes for thousands of kilometres, before connecting with the Sun again.
A new study says that some of what we are seeing isn't loops at all. They are a type of optical illusion. Do we know the Sun as well as we think we do?
The Sun's corona is the lowest part of the atmosphere. It's made from a substance that contains a lot of charged particles. That means that it responds quickly. The magnetic field on the Sun varies by time and place. Sometimes that magnetism drives the plasma high above the corona, forming fanciful structures called coronal loops that eventually connect to the Sun's surface. Some of these structures can last a long time.
“This is an entirely new paradigm of understanding the Sun’s atmosphere.”
Anna Malanushenko, lead author.
If the new study is correct, it means that many of the loops are not loops.
There is a new study in the Astrophysical Journal. The lead author is a scientist at the National Center for Atmospheric Research.
The study is based on a simulation of the Sun's corona. Scientists were able to separate individual loops by slicing the corona into sections. The researchers found a few loops, but many of them weren't loops at all.
The lead author said that he was excited that the simulation would give him the chance to study them in more detail. I didn't think this would happen. My mind exploded when I saw the results. This is a completely new way of understanding the Sun's atmosphere.
The coronal loops are bright due to their temperature. Their shape matches our understanding of magnetism, so concluding that they are loops is logical. The new study doesn't completely deny the existence of loops. It refutes some of them.
Scientists are looking at the Sun and its behavior again. The authors of the paper are confused because the loops don't match what they know about magnetism.
The Sun's magnetic field lines are strong, but they have to weaken further from the source. If the loops are real, they should be spread apart further from the Sun. That isn't what happens. Even high above the Sun, the loops are still thin and bright.
The authors point out in their paper that the corona's magnetic field weakens with altitude as the visual expansion of the loops is not expected.
So if they are not loops, what are they?
The authors are questioning what they knew about the Sun because of their existence.
This study reminds us that we must always question our assumptions and that sometimes our intuition can work against us.
Some of the loops are called projection artifacts. It is difficult to discern between the actual loops and artifacts. The authors show how isolated loops can deceive observers even when they have multiple viewing angles.
This research is based on a simulation that was developed at NCAR/UCAR. The simulation is called MURaM. Up to almost 40,000 km into the corona is where MURaM is a realistic simulation that extends from deep inside the Sun. The physical conditions in that wide range are not the same. Scientists hadn't been able to model such a wide range of conditions before it was developed.
Scientists were able to observe the entire life cycle of a solar flare, starting from deep within the Sun to the flare's emergence on the surface to its explosion into space.
The data set created by MURaM is the main result of this study. The data sets contain the magnetic field and its structure. The Sun's corona is easy to see through, thanks to the fact that it is very thin. That might sound like an observational advantage, but it isn't.
When we observe the Sun, structures like coronal loops can overlap. It is difficult to tell which is in the foreground and which is in the background. It is difficult to discern how thick the loops are because of the optical thinness. Are they like a garden hose? Are they thin like a ribbon?
There is a third possibility when looking at the loops in the corona. A fold in a sheet of plasma could cause loops to be an optical illusion.
One of the most powerful solar simulations has been created. Researchers are still cautious despite the fact that it has proven robust in many ways. The team compared the data from the MURaM instrument with the images from the SDO.
The simulation's strength is that it is possible for researchers to understand the data in a way that is not possible with actual observations. Current observatories and instruments can't study the Sun in a way that MURaM can.
Scientists assume that the loops are plane-of-sky projections of thin magnetic flux tubes full of different temperatures and densities because they conform to field lines. It could be a different temperature that doesn't show up well in the wavelength of the instrument.
The authors looked at the emission to see the fainter areas. The researchers were able to look for structures and behavior that weren't seen in real images with the help of thin slices of MURaM. The slices show that some of the loops are not loops at all, but ridges andwrinkles in the plasma.
The study raises questions about our understanding of the Sun. The study is based on a simulation. As time goes on, simulations play a more significant role in astronomy and astrophysics.
Can we trust him?
MURaM is one of the most realistic simulations to date according to the authors. We know this because we can see many things about the Sun. They believe that our results are relevant to the corona.
The results of the simulation that produced the conclusion of the study are compelling.
A study from 2005 found that the footprint of some coronal loops were wrinkled and not simple.
Emissions that don't look like loops were found in another study. Images from that simulation showed a diffuse component, several isolated blobs, and thin, bright, sheet-like structures similar to what MURaM showed in this new research. The loops that looked like projection artifacts were produced by the wrinkling of those sheet-like structures.
How many of the loops are actually loops, and how many aren't? New observational techniques will have to be designed. New data handling techniques are required. A better understanding of solar physics can be achieved by answering the question.
The study shows that the way we currently interpret the Sun's observations may not be enough for us to truly understand the physics of our star.
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