Sun's core rotates faster than surface
Astronomers observing the Sun have concluded that its core rotates faster than its surface; a conclusion that could help piece together the story of the Sun's formation.
The core of the Sun rotates almost four times as quick as the solar surface, according to a new study. A team of scientists made the conclusion by measuring the time it takes an acoustic wave to travel from the surface of the Sun and back again. The results could help astronomers piece together a model of how our host star formed.
Scientists had previously assumed the core was rotating at about the same speed as the surface.
But the new results suggest that, after the Sun formed, streams of particles called solar winds may have slowed the rotation of the outer part of the Sun.
The team arrived at this conclusion by studying surface acoustic waves in the Sun’s atmosphere.
These acoustic waves are produced by the plasma in the Sun’s convective zone.
Some of them penetrate to the Sun’s core, where they interact with gravity waves.
By measuring the acoustic waves in the Sun, the scientists determined the time it takes one to travel from the surface of the Sun to its centre, and back again.
This travel time is influenced slightly by the motions of the gravity waves.
The team identified the movements of the gravity waves and made their calculations using 16 years of observations by NASA’s Solar and Heliospheric Observatory.
“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,” says Roger Ulrich, a UCLA professor emeritus of astronomy and co-author of the study.
“It’s a surprise, and exciting to think we might have uncovered a relic of what the Sun was like when it first formed.”
Iain Todd is BBC Sky at Night Magazine's Staff Writer. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.