It is almost impossible to overemphasize a star’s primal, raging, natural power. Our Sun may seem harmless in simple observations, but with the advanced scientific tools at our disposal today, we know otherwise. When observed outside the narrow band of light our eyes can see, the Sun appears as an angry ball, occasionally hurling huge jets of plasma into space, some of which crash into Earth.
Plasma jets hitting the ground isn’t something to celebrate (unless you belong to some weird cult). it can cause all sorts of problems.
Some scientists devote themselves to studying the sun, in part because of the danger it poses. It would be nice to know when the sun throws a tantrum and if we’re in its way. We have several spaceships dedicated to detailed exploration of the sun. 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 Solar Dynamics Observatory (l), the Solar and Heliospheric Observatory (m) and the Parker Solar Probe (r.) Credit: Left: NASA. Middle: By Cgruda – http://sohowww.nascom.nasa.gov/gallery/images/SOHOLower2.htmlFile:SOHO nasa.tif, Public Domain, https://commons.wikimedia.org/w/index.php?curid =28983655. Right: NASA
The Sun’s powerful magnetic fields play a big part in the solar flares, though scientists are still working on the details. A new study published in Nature Astronomy is helping scientists understand magnetic fields in more detail. It is titled “Numerical evidence for a small dynamo approaching the solar-magnetic Prandtl numbers,” and the first author is Jörn Warnecke, a senior postdoctoral researcher at the Max Planck Institute for Solar System Research (MPS).
The solar dynamo is responsible for the sun’s magnetic fields. The solar dynamo consists of two parts: the small dynamo and the large dynamo. The problem is that solar researchers have not yet been able to model them, at least not in great detail. Trouble is, they can’t confirm that a small-scale dynamo (SSD), which is ubiquitous in astrophysical bodies across the Universe, can even be generated by conditions in the Sun. This is obviously a big problem, because a small dynamo would have a big impact on how the sun behaves.
“A powerful SSD can potentially have a major impact on the dynamic processes in the sun,” the authors write in their article. “Therefore, it is of great importance to clarify whether an SSD can exist in the Sun or not.”
What is a small dynamo?
According to this study, a small dynamo amplifies magnetic fields at magnitudes smaller than the magnitude driving turbulence in various astrophysical media. It’s easy to go astray trying to understand this in detail. But in very simple terms, an SSD requires much more turbulence than a large dynamo.
It all depends on what is called a Prandtl number (PrN,) and what the Prandtl number of the sun tells us about its properties. The Sun’s PrN tells us how quickly its magnetic field fluctuations and speed even out. The Sun has a low PrN, and scientists studying the Sun have long thought that the low value prevented the development of an SSD.
But this research shows otherwise. It is based on extensive computer simulations on petascale supercomputers in Finland and Germany.
This figure from the study is a visualization of the flow and the SSD solution. Flow velocity is on the left, magnetic field strength on the right. This simulation run showed a very low Prandt number. “As expected in low PrM turbulence, the flow exhibits much finer, fractal-like structures than the magnetic field,” the authors explain. Image source: Warnecke et al. 2023
“Using one of the largest possible computer simulations currently available, we have achieved the most realistic environment for modeling this dynamo to date,” says Maarit Korpi-Lagg, group leader in astroinformatics and associate professor in the Computer Science Department at Aalto University. “We have not only shown that the small dynamo exists, but also that the more our model resembles the sun, the more practical it becomes.”
Low values for the Prandtl number mean that the plasma velocity and the magnetic field fluctuation in the sun quickly balance out. And the faster they equalize, the less likely it is that an SSD can form. By finding that this is not the case, and that conditions on the Sun can produce an SSD, scientists’ understanding of the Sun, its magnetic fields, and its plasma ejecta only increases. And that’s good for us, living on a planet that’s right in the path of some solar ejection.
Coronal Mass Ejections (CME) observed by the Solar Dynamics Observatory on June 7, 2011. CMEs eject plasma from the Sun’s corona. Image Credit: NASA/SDO
“This is a big step towards understanding the magnetic field generation in the Sun and other stars,” says Jörn Warnecke, senior postdoc at the MPS. “This result will bring us closer to solving the mystery of CME formation, which is important to protect Earth from dangerous space weather.”
As many Universe Today readers know, the Sun follows an 11-year cycle that determines its magnetic fields. Every 11 years, the sun’s poles switch places, and that changes the sun’s behavior. Flares, solar flares, and coronal mass ejections increase in mid-cycle, known as Solar Maximum. Because solar flares can disrupt communications, power grids, and other infrastructure on Earth, scientists want to better understand it.
This image represents a current 11-year solar cycle and shows the Sun in ultraviolet light. The solar maximum is in the middle of the cycle, when the sun shows significantly more activity. Photo Credit: Dan Seaton/European Space Agency (Collage by NOAA/JPL-Caltech)
The interactions between SSD and LSD create the solar cycle, so these findings help to better understand solar weather and when to expect chaos to come.