Sun's Core Rotates Slower Than Previously Thought

It seems that the solar core rotation is slower than previous theories suggested.

The core of the Sun is extending from the center to about 0.2 of the solar radius, and it's the hottest and most dense part of the Sun, having a temperature of 15 million Kelvins (the surface only has 6 000 K) and a density 150 times greater than that of water.

Not many things are known about the core, except the fact that it's the place where energy is produced by exothermic thermonuclear reactions (nuclear fusion) that mainly convert hydrogen into helium, around 400 tons of hydrogen being fused together to form helium, thus producing light, heat and other forms of radiation, both beneficial and dangerous for life on Earth.

So far, the core has been very difficult to explore, since the outer layers eclipse all the readings coming from the center. It contains secrets into how it and the planets formed billions of years ago, but the bright solar surface obscures the view of its heart and the only way to take a look at what's inside is to study the waves on the solar surface, generated by sound running through the Sun.

That's exactly what an international team of astronomers employing the ESA-NASA Solar and Heliospheric Observatory (SOHO) has done, by studying the "p-mode" waves, ever since they first discovered them, some 30 years ago and up to now.

These waves give the best clues at the existence of far more subtle ripples driven by gravity, called "g-mode" waves. In turn, these are believed to occur when gas churning below the surface plunges even deeper and collides with denser material, sending ripples propagating through the interior and up to the surface, the equivalent of dropping a stone in a pond, but in space.

Since g-mode waves pass through the Sun's mysterious heart, they carry vital information concerning internal activity. For example, the speed at which the solar core rotates is uncertain. Knowing this detail could shed light on the birth of the entire solar system, because it represents the hub of rotation for the dusty cloud of matter that eventually formed the sun and planets.

So, astrophysicist Rafael Garcia at DSM/DAPNIA/Service d'Astrophysique in France and his colleagues looked for the signature of a large number of these oscillations from 10 years of data.

The core's rotation speed is best indicated by the way the g-modes got distorted as they pass through the Sun. The distortions are partly due to the fact that the surface of the Sun rotates at different rates depending on location, with the equator spinning faster (about 25 days) than the poles (roughly 36 days).

The final result of the analysis indicated that "The core of the Sun seems to rotate about three to five times faster on average," as Garcia concluded.