It’s nearly impossible to overemphasize a star’s primal, raging, natural power. Our Sun may seem benign in simple observations, but with the advanced scientific tools at our disposal in modern times, we know otherwise. In observations outside the narrow band of light that our eyes can see, the Sun appears as a raging, raging sphere, occasionally hurling huge jets of plasma into space, some of which strike the Earth.
Plasma jets hitting Earth aren’t something to celebrate (unless you’re in a weird cult); it can cause all kinds of problems.
Some scientists are dedicated to studying the Sun, in part because of the danger it poses. It would be nice to know when the Sun will throw a tantrum and if we will be in its path. We have multiple spacecraft dedicated to studying the Sun in detail. The Solar Dynamics Observatory (SDO), the Solar and Heliospheric Observatory (SOHO), and the Parker Solar Probe are all engaged in solar observations.
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The sun’s powerful magnetic fields play a huge role in the sun’s outbursts, although scientists are still working out the details. A new study published in Nature Astronomy is helping scientists understand magnetic fields in more detail. It’s titled “Numerical Evidence for a Small-Scale Dynamo Approaching Solar Magnetic Prandtl Numbers,” and the first author is Jrn Warnecke, a postdoctoral researcher at the Max Planck Institute for Solar System Research (MPS).
The solar dynamo is responsible for the magnetic fields of the Sun. The solar dynamo has two parts: the small-scale dynamo and the large-scale dynamo. The problem is, solar researchers haven’t yet been able to model them, at least not in all the detail. Problematically, they cannot confirm that a small-scale dynamo (SSD), which is ubiquitous in astrophysical bodies throughout the Universe, can also be generated by conditions on the Sun. This is obviously a big deal because a small-scale dynamo would have a enormous influence on the behavior of the Sun.
“A powerful SSD can potentially have a big impact on dynamic processes in the Sun,” the authors write in their paper. “So, it is of great importance to clarify whether or not an SSD can exist in the Sun.”
What is a small-scale dynamo?
A small-scale dynamo amplifies magnetic fields to scales smaller than the guide scale of turbulence in several astrophysical media, according to this study. You can quickly go down the rabbit hole trying to figure this out in detail. But in simple enough terms, an SSD requires much stronger turbulence than a full-scale dynamo.
It all comes down to what is called a Prandtl number (PrN) and what the Sun’s Prandtl number tells us about its properties. The Sun’s PrN tells us how fast its magnetic field changes and its velocity equalizes. The Sun has a low PrN, and for a long time, scientists studying the Sun thought that the low number prevented the development of an SSD.
But this research shows otherwise. It is based on massive computer simulations on petascale supercomputers in Finland and Germany.
“Using one of the largest possible computational simulations currently available, we have achieved the most realistic environment to date in which to model this dynamo,” says Maarit Korpi-Lagg, astroinformatics group leader and associate professor in the Department of Computer Science at the Aalto University. “We have shown not only that the small-scale dynamo exists, but also that it becomes more feasible as our model looks more like the Sun.”
Low values for the Prandtl number mean that the plasma velocity and magnetic field change rapidly equalize across the Sun. And the faster they equalize, the more unlikely it is that an SSD will form. By discovering that this is not the case and that conditions on the Sun can generate an SSD, scientists’ understanding of the Sun, its magnetic fields and its plasma ejections only increases. And that’s good for us who live on a planet directly in the path of some of the Sun’s ejections.
“This is an important step toward understanding magnetic field generation in the Sun and other stars,” says Jrn Warnecke, senior postdoctoral researcher at MPS. “This result will bring us closer to solving the puzzle of CME formation, which is important for devising protection for Earth against dangerous space weather.”
Many Universe Today readers know that the Sun operates on an 11-year cycle that governs its magnetic fields. Every 11 years the Sun’s poles switch places and this changes the behavior of the Sun. Flares, solar flares and coronal mass ejections increase during the middle of the cycle, called the solar maximum. Because flares from the Sun can disrupt communications, power grids, and other infrastructure on Earth, scientists would like to understand this better.
The interactions between SSD and LSD create the solar cycle, so these findings contribute to a better understanding of solar weather and when we might expect chaos to come.
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