The Sun’s Core Spins Roughly Four Times Faster Than Its Surface

Within the fiery heart of the sun is a dense core spinning nearly four times faster than the star's surface, according to new measurements.

The roots of the solar system lie in a spinning disk of hot gas and dust that began to coalesce more than 4.5 billion years ago. One legacy of that disk's spin is the rotation of our Sun. But unlike the rocky planets, different parts of this flaming ball of gas and plasma rotate at different rates. At its equator, the sun completes one rotation every 27 Earth days. It takes even longer at the poles. 

"There have been some earlier suspicions of the sun going at a different rate in its core, but they were very speculative and very tentative," Roger Ulrich, an astronomer at the University of California, Los Angeles, tells Smithsonian.com. But scientists had no direct way of measuring inside of the sun to test if this were true.

But Ulrich's and his team found a way around this problem. The researchers drew on more than 16 years of data from the ​Solar and Heliospheric Observatory​ (SOHO) satellite, which circles the sun along with the Earth, observing the sun in an attempt to demistify this flaming ball of gas and plasma. Along with other measures, the SOHO satellite tracks solar sound waves that have traveled the more than 400,000 miles from inside the sun to its surface. On that long journey, the sound waves are influenced by waves of gravity, which cause almost a "sloshing motion," reports David Grossman for Popular Mechanics.

By calculating how much the sound waves were distorted by gravity, researchers were able to estimate how rapidly the Sun's core was rotating, reports Brooks Hays for UPI. Unlike the conventional beliefs that the core's rotation speed roughly matched that of the surface, it turns out that the Sun's core spins about four times faster. The researchers published their results in the journal Astronomy and Astrophysics.

"The most likely explanation is that this core rotation is left over from the period when the sun formed, some 4.6 billion years ago," astronomer Roger Ulrich, co-author of the study, says in a statement. The sun likely rotated much faster around when it was formed, Ulrich says. But over the millennia solar winds likely created drag on the surface, slowing its external rotation. “It’s a surprise, and exciting to think we might have uncovered a relic of what the sun was like when it first formed," says Ulrich.

Next, the researchers hope to confirm these estimates with data collected from other space instruments like the SOHO satellite or the Solar Dynamics Observatory.

The calculations also revealed the hellish temperatures one would find in the core of the Sun, which can reach some 29 million degrees Fahrenheit, compared to a relatively "cool" 10,000 degrees Fahrenheit on the star's surface.

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Ben Panko is a staff writer for Smithsonian.com