spaceSpace and Physics

The Sun Is Changing Shape And We're Not Sure Why


Robin Andrews

Science & Policy Writer

The Sun and some of its magnetic field lines overlaid on top. NASA Goddard/SDO

It’s true that our local star is a fairly average star, relative to all the others we know of in the deep and beautiful dark up there. It is, however, still an absolutely exhilarating little nuclear reactor, producing pseudo-tornadoes and solar flares, and sending intricate streams of plasma off into the night.

A new study, spotted by New Scientist, adds another remarkable layer to the furnace that makes everything possible. According to a new paper in The Astrophysical Journal, the Sun grows and shrinks every 11 years by 1 to 2 kilometers (0.6-1.2 miles). Colloquially, you could very well say that it breathes, albeit very slowly.


It’s a very faint “inhale” and “exhale” though, with those extra kilometers increasing the radius of the Sun by just 0.00029 percent at most. With that in mind, then, it’s incredible that the team from the New Jersey Institute of Technology and the University of Cote d’Azur managed to detect it at all. So how did they?

As with several recent studies, the team zeroed in on the plasma streams escaping and returning to the solar surface – highly energetic ionized gas strands. Turns out that the frequencies of the plasma waves that slosh across the star aren’t too dissimilar from the sound waves given off by a musical instrument.

Say you’ve got a saxophone, because you fancy some jazz. You play a note, noise comes out, and all’s well. Now, if the tubing inside the saxophone suddenly expanded outwards, the pitch of that note would drop. Squeeze it all in, and the pitch would be higher.

The Sun’s a bit like a magical saxophone in that sense. The frequencies of those waves change depending on how sizeable the Sun is, and this can be measured rather precisely by scientists on Earth. It wasn’t easy, though; after all it did take 21 years of observations using two separate NASA space telescopes to make this discovery.


Eagle-eyed solar science types among you may have already guessed what the “breathing” is related to, and you’d be right: it’s to do with the solar cycle.

Every 11 years, the Sun moves from a violent solar maximum to a tranquil-ish solar minimum. At a maximum, sunspots – dark patches of intense magnetic activity – appear more frequently and cluster just above and below the equator.

More sunspots up the chances of solar storms appearing, which could mean anything from more potent aurorae in our skies to malfunctioning electrical infrastructure. At a minimum, sunspots become more of a rarity.

This activity is driven by the magnetic activity buried deep within the Sun. Indeed, the plasma waves that the team were tracking swim beneath the surface too on the order of several million meters, near to the radius of Earth in terms of distance.


The Sun expands a little during the minimum, and contracts during the maximum. Although the team note that there is currently “no theory” that links the displacements to changes in the internal magnetic machinations of the Sun, they suggest that it’s linked to the change in the orientation of the magnetic fields that occur over the cycle.

The field of research is known by an extremely cool name, by the way: helioseismology, which is essentially the equivalent of terrestrial seismology – like listening to faults move or volcanic tremors – but in space.

Just in case you were wondering: no, this incredibly small change in solar dimensions does not affect the climate here on Earth. We still have to deal with anthropogenic climate change. Let’s nip that one in the bud right there, and never speak of it again.


spaceSpace and Physics
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