The Sun’s Mysteries: Unraveling Solar Secrets with Cutting-Edge Research

The Sun, our closest star, is the foundation of life on Earth. Despite centuries of study, fundamental mysteries continue to challenge solar physicists. Among these are the eleven-year solar cycle, the inexplicable heating of the corona to millions of degrees Celsius – far hotter than the surface temperature of 6,000 degrees Celsius – and the driving force behind the solar wind, a constant stream of charged particles.

Researchers at the University of Oslo are actively pursuing answers, utilizing ground-based telescopes with extreme resolution and powerful supercomputers to unravel the Sun’s secrets. “We are piecing together the puzzle, bit by bit,” says Mats Carlsson, professor at the Department of Theoretical Astrophysics and head of the Rosseland Centre for Solar Physics, a leading research center. “We’ve made new discoveries and come a long way.” The center is a world leader in using high-performance computing to simulate how the Sun functions and how it can impact life on Earth.

“Insights from our own star can explain phenomena throughout the cosmos and provide a unique laboratory for understanding stars, black holes, and neutron stars,” adds his colleague, Professor Luc Rouppe van der Voort. “We can’t see the details in distant stars, but we can see those details on the Sun. What we learn there applies to the entire universe.”

Solflekkenes mørke mysterium (The Dark Mystery of Sunspots)

One of the Sun’s peculiar phenomena is sunspots, the locations of the largest solar flares. These active regions are where plasma can erupt at enormous speeds towards Earth. Sunspots aren’t always neat and round; they can be oval or clustered together. Crucially, they are cooler than the surrounding solar surface – though still incredibly hot, at around 4,000 degrees Celsius.

The explanation for this relative ‘coolness’ lies in the incredibly strong magnetic fields within sunspots. “These strong magnetic fields suppress the flow of hot plasma rising from the Sun’s interior,” explains Rouppe van der Voort. While magnetic fields are invisible, their influence can be studied by observing the shape of the plasma that follows them.

Magnetic fields can connect two sunspots with opposite polarities – a positive and a negative – forming a loop resembling an inverted U. These connected spots are bound by the same magnetic field. The most explosive spots can contain areas where positive and negative polarities mix, creating chaotic magnetic fields and increasing the risk of large eruptions. “Large, chaotic sunspots are generally more dangerous than neat, round ones,” Rouppe van der Voort points out.

When magnetic field lines collide and reconnect within sunspots, it can trigger enormous explosions. Rebecca Nguyen, a master’s student, explains this process: “It’s like pulling and releasing a rubber band – it snaps.” When these explosions are powerful enough, the energy released flings plasma into space, potentially impacting Earth.

“Telys”-eksplosjoner (”Tealight” Explosions)

In contrast to the relatively infrequent and large sunspots, the Sun is teeming with small, short-lived explosions. These appear as small flares, lasting just three to five minutes. Up close, these “tealights” are 100 to 200 kilometers wide and 1,000 to 2,000 kilometers high.

First described in 1917 by American astronomer Ferdinand Ellerman, these events, initially called hydrogen bombs due to their spectral signature, are now known as Ellerman bombs. Carlsson notes that these bombs are far more common than previously thought. They may hold the key to understanding the Sun’s explosive nature.

“We used to think these bombs were only found in active regions around sunspots,” says Rouppe van der Voort. “But now we know they also exist in the quiet parts of the Sun. In fact, it’s estimated that around 750,000 such Ellerman bombs exist on the Sun at any given time.”

Researchers at the University of Oslo are at the forefront of studying this phenomenon. These small explosions may help regulate the magnetic stress that builds up within the Sun, acting as “valves” to release pressure. While speculative, this theory is gaining traction.

Without Ellerman bombs, solar eruptions might be far more powerful. Studying them is a crucial piece of the puzzle in understanding solar magnetism and predicting space weather events.

Lydbølger (Sound Waves)

In addition to studying visible phenomena, astrophysicists, in collaboration with the Max Planck Institute in Göttingen, Germany, are also investigating sound waves within the Sun. This field, known as helioseismology, allows them to map the Sun’s interior, measuring its rotation, gas flow speeds, and distribution. Sound waves travel into the Sun and are reflected back, with different frequencies corresponding to different depths.

“By looking at how many times the sound waves have traveled up and down around the Sun, we get a picture of how far into the Sun they have been,” explains Carlsson. “The observations don’t quite match the simulations. When something doesn’t match, we need to change the models.”

Målinger fra rommet (Measurements from Space)

While ground-based telescopes offer high resolution, observing the Sun from space provides continuous data, albeit with lower resolution. Satellites like IRIS, SDO, and Solar Orbiter provide complementary data, allowing researchers to combine observations from different layers of the solar atmosphere for a more complete picture.

The upcoming MUSE satellite, planned by NASA and ESA, promises to capture images 35 times faster than current satellites, potentially revealing more detailed insights into solar explosions. Researchers are developing machine learning methods to process the data from MUSE efficiently.

Matematiske modeller (Mathematical Models)

Researchers have created massive simulation models of the Sun’s upper layers, while the French CEA institute models the interior. They are now working to connect these models, a complex task requiring immense computational power. These simulations can now calculate what happens on the Sun in real-time – a one-hour simulation takes one hour of computing time. This is a significant improvement, considering the eleven-year solar cycle.

“Our goal is to understand how the magnetic field works in the Sun and in astrophysical plasma,” says Rouppe van der Voort. “The same phenomenon occurs in other stars, and in neutron stars and black holes. We can therefore use the Sun as a laboratory to understand other stars and other processes in the universe.”