Celestial Sound Waves Reveal Surprising Solar Changes

July 11, 2017

The celestial music released from the sun suggests that its outer layer has grown weaker over the years, according to new research from the United Kingdom.

The sun releases sound waves, and like a musical instrument, the structure of the sun informs the way the sound waves are shaped. Scientists can study the sun’s oscillations by listening to the frequencies that make up the sound signal, thereby learning something about the object making the sound. Because the waves are generated by and pass through different sections of the sun, the wave frequency reveals clues about the inside of the sun and allows scientists to chart changes in the star’s life.

Scientists from the Birmingham Solar-Oscillations Network at the University of Birmingham, in the United Kingdom, used the sun’s sound waves to determine that one of its outermost layers may be growing thinner. [How the Sun’s Magnetic Field Works (Infographic)]

“The sun is the only star on which we can get this level of detail,” Yvonne Elsworth, a researcher working on the project at the University of Birmingham, told Space.com in an email. “Other stars do show activity cycles, and if we can understand the processes in the sun, we will be able to extend the ideas to other stars.”

“The study of the sun is crucial to scientists’ understanding of the cosmos because it is the closest star to our planet, and learning about its life processes reveals more about the dynamics of stars many light-years away,” she added.

Elsworth presented the new research at the National Astronomy Meeting at the University of Hull in the United Kingdom on July 4.

Tracking the waves

The sun, like Earth, has different layers. One of the outermost layers is a few hundred kilometers wide, according to NASA, and is made up of plasma. The sun’s plasma is a tremendously hot mix of separated electrons and ions, which means they are charged and naturally create magnetic fields. Plasma churns and pulls in different directions around the sun, and the enormous heat produced by the nuclear fission at the core plays along these currents to create magnetic fields.

So how does the sun produce sound? The movement of the plasma creates sound waves. Patches on the surface of the sun oscillate up and down in 5-minute motions, NASA officials said in a reference page. These sound waves travel radially, meaning inward and outward. The sound waves remain inside the sun, because the cavity of the star is constrained by the properties of its surface, thereby sending the waves downward. Then, a change of direction caused by the wave’s increased speed toward the middle of the sun makes it bounce back up toward the surface. When scientists study the frequency of these waves, they can tell a lot about the inside of the star, as well as learn about its magnetic field. This is called helioseismology, and as the name suggests, it is similar to the concept of studying subterranean waves on Earth to predict earthquakes.

Solar sound waves are much too low for humans to hear, but they can be detected visually on the sun’s surface and analyzed (as in this explanatory video). Visible features are caused by sound waves deep inside the sun’s core, and they are simultaneously shaped by the activity near the solar surface.

Because these features are influenced by both the sun’s core and the area near its surface, studying the features gives scientists a big picture look at the sun, researchers said in a statement about the new work. This allows them to learn about the changing physical conditions of the sun, either at a given moment or over many years.

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