How solar prominences form

The new computer simulations are based on a magnetic field structure that is often associated with prominences: the magnetic field lines in the corona form a double arc with a small dip in the middle. As the calculations show, the flame-like prominence forms in this dip and remains trapped there. All relevant layers of the Sun were taken into account, from the corona, the Sun’s outer atmosphere, to parts of the convection zone below the Sun’s surface.
Image Credit: © MPS

Scientific Frontline: Extended "At a Glance" Summary: Solar Prominence Supply Mechanisms

The Core Concept: Solar prominences are massive, densely packed structures of relatively cool plasma that extend for thousands of kilometers into the Sun's exceptionally hot outer atmosphere, the corona.

Key Distinction/Mechanism: Unlike the surrounding corona, which burns at over one million degrees, prominences consist of plasma cooled to approximately 10,000 degrees. They remain suspended and stable for weeks due to a delicate supply balance: turbulent magnetic forces in the cooler, lower layer of the Sun (the chromosphere) eject bursts of cool plasma upward, while hot coronal plasma simultaneously flows into magnetic dips and condenses, offsetting material that "rains" back down.

Major Frameworks/Components:

• Double-Arc Magnetic Architecture: Magnetic field lines in the corona frequently form a double arch resembling two adjacent mountains; the cool prominence material forms and becomes trapped within the central dip.
• Chromospheric Injection: Turbulent, small-scale magnetic field movements beneath the corona forcefully eject cool plasma upward to feed the prominence.
• Coronal Condensation: Secondary supply logistics occur when hot plasma travels along magnetic field lines into the central dip, where it cools and condenses.
• Multi-Layered Simulation Models: The research framework accounts for all relevant solar layers concurrently, linking turbulent plasma flows below the visible surface, the cooler chromosphere, and the extremely hot corona.

Branch of Science: Heliophysics, Solar Physics, and Magnetohydrodynamics

Future Application: The integration of these supply mechanisms into advanced computational models will vastly improve space weather forecasting, allowing for earlier and more accurate predictions of solar eruptions.

Why It Matters: Prominences possess immense explosive potential; if they destabilize, they can hurl charged particles into space, triggering severe solar storms. Understanding their structural longevity and eruption triggers is vital for protecting Earth's critical infrastructure, including power grids, telecommunications, and satellite networks.

Solar prominences come in a wide variety of shapes and sizes—sometimes even simultaneously, as this image of the Sun from February 11, 2014, impressively demonstrates. While most prominences resemble billowing flames, others take on a loop-like shape. Prominences at the edge of the Sun appear bright to the observer, while those on the solar disk appear dark.
Image Credit: © Sun: NASA/SDO/GSFC Visualization Studio/Virtual Solar Observatory; white frames: MPS

Large amounts of matter are needed to create and sustain the massive plasma structures in the solar corona. New calculations reveal how this is possible 

At more than one million degrees, the Sun’s atmosphere, the corona, is incredibly hot. However, not everywhere. Time and again, huge structures of significantly cooler solar plasma - about 10,000 degrees - appear within the corona. These structures are known as prominences. They span up to several thousand kilometers and often resemble flickering flames that can take on a wide variety of shapes. Despite their delicate appearance, they are massive “chunks of matter”: their density exceeds that of the surrounding corona by more than a hundred. In a sense, this is as if a giant mountain were suspended in mid-air. Prominences can remain stable for weeks or even months, yet they also possess explosive potential: if they do not fade away quietly, they culminate in a massive eruption during which the Sun hurls charged particles into space. If the particle cloud spreads toward Earth, it can trigger violent solar storms. 

In the current publication in the journal Nature Astronomy, researchers at the Max Planck Institute for Solar System Research (MPS) in Germany investigate how prominences form and what the secret of their longevity is. Their findings reveal that multiple processes are at work, creating a constant balance between material loss and supply. 

In complex computer simulations, the researchers model the interaction of magnetic fields and plasma within the Sun. In doing so, they consider not only the Sun’s atmosphere, where the prominences manifest, but for the first time also the deeper, cooler layers of our star. There, beneath the Sun’s visible surface, turbulent plasma flows generate the Sun’s complex, constantly changing magnetic field, which extends even into the corona. 

To protect Earth’s infrastructure in time, reliable forecasts of dangerous space weather are needed. A deeper understanding of prominences is a crucial piece of the puzzle. 

“In the Sun’s atmosphere, the magnetic field is the driving force. It also plays a decisive role in all processes that contribute to the formation and maintenance of the prominences,” says MPS scientist Lisa-Marie Zeßner-Ondratschek, first author of the new publication. Equally decisive is the temperature gradient within these layers. With a maximum temperature of 20,000 degrees, the lower solar atmosphere, the chromosphere, is significantly cooler than the corona; the underlying solar surface reaches just 6,000 degrees. 

A sequence of images from the new computer simulations. The flame-like prominence extends up to about 20,000 kilometers into the corona and constantly changes shape. Occasionally, some of its material “rains” back down into the Sun’s lower-laying layers (image D).
Image Credit: © MPS

Trapped in the magnetic field dip 

For her calculations, the researcher focused on the smaller prominences, which extend “only” up to 20,000 kilometers into the corona. She assumed a magnetic field architecture that often accompanies prominences: the magnetic field lines take the form of a double arch in the corona. They resemble the two humps of a dromedary or two adjacent mountains in a mountain range. The prominence forms in the dip between the “humps.” 

As the computer simulations show, a kind of injection process sets the prominence in motion. Driven by turbulent, small-scale magnetic field movements, the chromosphere ejects bursts of cool plasma; this billowing blob remains trapped in the magnetic field dip in the corona. Then the sophisticated supply logistics of the prominences kick in: Although some of the cool plasma repeatedly “rains” back down into lower-lying layers, two processes compensate for the losses: Material is regularly ejected from the chromosphere; additionally - albeit to a lesser extent - hot plasma flows from the corona along the magnetic field lines into the dip, cools down, and “condenses” there. 

“Our calculations show, more realistically than ever before, how both processes interact to supply the prominences with material and thus keep them alive,” says Lisa-Marie Zeßner-Ondratschek. Earlier simulations, which had only taken the Sun’s atmosphere into account, were mainly able to model condensation in the corona. The new publication thus closes a major gap in our knowledge and impressively demonstrates that processes within the Sun’s interior are also crucial for understanding - and perhaps one day predicting - the eruptive nature of our star. 

Published in journal: Nature Astronomy

Title: Self-consistent numerical simulations for the formation and dynamics of solar prominences

Authors: Lisa-Marie Zessner, Robert H. Cameron, Sami K. Solanki, and Damien Przybylski

Source/Credit: Max-Planck-Gesellschaft

Reference Number: heli042226_01

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