Not so smooth: "Cantaloupe ridges" on the Sun. The glowing white magnetic network is what decreases the roundness of the Sun during times of high solar activity. (Los Angeles astronomer Gary Palmer took this picture in 2005, using a violet calcium-K solar filter.)
Credit: NASA/Gary Palmer
The scientists further found that the rough ridges are magnetic in nature; they outline giant, bubbling convection cells on the surface of the Sun called 'supergranules'. These are like bubbles in a pot of boiling water amplified to the scale of a star – on the Sun they measure some 30,000 km across (twice as wide as Earth) and are made of seething hot, magnetised plasma.
Magnetic fields at the centre of these bubbles are swept out to the edge where they form ridges of magnetism. The ridges are most prominent during periods of years around the solar maximum, says the study, when the Sun's inner dynamo produces the strongest magnetic fields.
Solar physicists have known about supergranules and the magnetic network they produce for many years, but only now has RHESSI revealed their unexpected connection to the Sun's equatorial width.
New frontier in solar physics
"These results have far-ranging implications for solar physics and theories of gravity," commented solar physicist David Hathaway of the NASA's Marshall Space Flight Centre in Huntsville, Alabama.
"They indicate that the core of the Sun cannot be rotating much more rapidly than the surface, and that [the differences between the polar and equatorial diameter of the Sun] is too small to change the orbit of Mercury outside the bounds of Einstein's General Theory of Relativity."
Further analysis of RHESSI data on the Sun's roundness could also help researchers detect a long-sought type of seismic wave echoing through the interior of the Sun: gravitational oscillations or 'g-modes'.
The ability to monitor g-modes would open a new frontier in solar physics—the study of the Sun's internal core, said Hathaway, who is not one of the study's authors.
Ridges of Magnetism?
Can someone please explain PRECISELY what a "ridge of magnetism" is? I don't suppose it's related to a "tube of electricity?"
But seriously. The statement seems to divorce magnetic fields from electric currents and treat the magnetic fields as a separate "substance" that exists independent of the electric currents required to generate them (and say that they can somehow "pile up in ridges"). "Magnetic ridges" seems to be a scientifically sloppy, non-rigorous phrase to me. One hopes it's from the science / press release writers and not from the investigating scientists themselves.
Are not electric currents required by Maxwell, Ampere, Faraday, et al, to account for magnetic fields? Also my understanding was that plasmas generally cannot be permanently magnetized, thus a current is required to sustain the magnetic fields we observe, yes?