Astronomers have looked at how oscillations propagate through the Sun to study what’s going on beneath the surface. And it appears that the Sun has undergone some changes with important consequences for the star as a whole.

The study, published in the Monthly Notices of the Royal Astronomical Society, indicates how the magnetic field distribution in the outer layers of our Sun appears to be getting thinner. The data, which goes back until 1985 suggests that interior of our star has changed a fair bit.

These changes might have had a crucial effect on the solar activity that repeats about every 11 years. The Sun's most active period, the maximum, was subdued in the latest cycle and the quiet period, the minimum, was longer than expected.

“Recent activity maxima have actually been rather quiet and the last cycle had a long, extended minimum,” senior author Professor Yvonne Elsworth, of the School of Physics and Astronomy at the University of Birmingham, said in a statement.

“It will be interesting to see if the minimum of this current cycle is extended in the manner of the previous one or if it will soon be back to the conditions of the past. However, if it is a normal minimum it will also be interesting to ask why the previous one was unusual.”

The research is being presented this week at the National Astronomy Meeting at the University of Hull by Professor Elsworth. The change in magnetic field is not the only difference that the researchers have seen in the data. The Sun, at certain latitudes, is not rotating like it used to.

“Again, this is not how it used to be and the rotation rate has slowed a bit at latitudes around about 60 degrees. We are not quite sure what the consequences of this will be but it’s clear that we are in unusual times. However, we are beginning to detect some features belonging to the next cycle and we can suggest that the next minimum will be in about two years,” added Elsworth.

This study was possible thanks to over three decades of solar oscillation recorded by the University of Birmingham. These oscillations are gigantic soundwaves moving through the Sun as its interior is shaken and stirred by the convection of plasma from the deeper layers.

“The Sun is very much like a musical instrument except that its typical notes are at a very low frequency – some 100,000 times lower than middle C. Studying these sound waves, using a technique called helioseismology, enables us to find out what’s going on throughout the Sun’s interior,” Elsworth remarked.

There’s still so much we don’t know about the Sun but this study provides some vital clue to get a better picture of our star.