Does the Sun Have an Off Switch?

Excerpted from chart 14 of Tapping 2010

The 10.7 cm solar flux has long been used as more scientifically reliable measurement of solar activity than the sunspot number (SSN). The two are roughly correlated, permitting continuity of data going back centuries to when the only relevant observable was SSN.

However the true measure of solar activity can range significantly higher, and lower, than what the SSN indicates. A simple correlation implies that when the SSN is zero the 10.7 cm solar flux is ~65, and would therefore represent the lowest possible level of solar activity. This is not quite true, and as the NOAA says the 10.7 cm solar flux can dip below 50.

A star core is a thermonuclear furnace with the outer layers behaving in accord with thermodynamics as it transports heat from fusion to surface by convection. Aside from magnetic turbulence and other episodic and periodic phenomena it is exceeding difficult to shift the sun from thermodynamic equilibrium. More precisely, the probability of deviation from the equilibrium point declines rapidly with distance and deviation duration becomes increasingly brief.

This brings us to the puzzle of NOAA's latest forecast of solar activity beyond the demise of cycle 24.

Here we see the smoothed solar flux not only dipping below 66 but going far lower and remaining there for the foreseeable future. Calling this exceedingly atypical is an understatement of the first order. Indeed, it is alarming. What is going on here? Are there hitherto undiscovered periodic or secular dynamics within the sun's interior? Inquiring minds want to know.

Now we must acknowledge that not everyone is on side with the NOAA forecast. One reviewer calls it "fatally flawed and an embarrassment to NOAA's scientists." While this may be true these same scientists have held to the published forecast for quite some time in the face of pointed criticism. There must be something to it, something they have yet to disclose. Whatever it is it has to be big, really big. Is it in fact possible to upset the thermal equilibrium of the photosphere for years?

Numerous scientists have been hard at work to develop the theoretical framework to explain the latest forecast. These have ranged from the mundane to the sublime, from the finding of errors in current models to new physics. While some of them delve into the unknown with unbridled enthusiasm they may be worthy of consideration since the impacts could be dire. After all, the health of the star at the centre of our solar system determines the fate of humanity and even the Earth.

One of these novel theories was recently proposed by Dr. Lance Boyle, an astrophysicist and accordion aficionado. He has some intriguing insights into the coming plunge in solar activity. But don't worry, he doesn't think the decline is permanent. He likens what is going on to a temperature inversion in our own atmosphere.

"There is tremendous turbulence in the sun below the photosphere," he explains, "that is driven by high-energy photons that are too far below the surface to radiate into space. This is much like our own atmosphere, but with heat from the nuclear furnace coming from below rather than from above. Sometimes convection cells deliver so much hot gas near the surface that they form a barrier preventing the cooler regions associated with sunspots from reaching the surface."

Cutting through the technical jargon he goes on to say that the sunspots are still there but are below the surface and unable to influence solar radiation. With a knowing look he claims, "the sunspot cycle is doing just fine even if we can't observe it directly. Cycle 26 will probably bring a return to normality once the turbulence, sub-solar storms if you will, break up the inversion."

A more radical theory, an outlandish one in the view of many solar astronomers, is credited to Dr. Suzy Sunshine -- an unexpectedly appropriate name for a scientist in the field -- who is a post-doctoral fellow studying stellar dynamics. Her theory relies on the fundamentals underlying the laws of thermodynamics. "The sun is mostly hydrogen, but it is only in the core where the temperature and pressure are just right for hydrogen fusion to take place."

She says there are countless collisions every second between hydrogen atoms in the sun's core, due to their high density and temperature. It's a thermal engine in an exquisite balance. "Too much fusion and the core expands to reduce collisions, while too little fusion and the core contracts to increase collisions. The sun's nuclear core is regulated by the balance between outward photonic pressure and inward gravitational pressure."

Thermodynamics is driven by probabilities, not by certainties. Those countless atoms of hydrogen have degrees of freedom in their seemingly random movements that can upset the balance. "Very few of those collisions between protons, the hydrogen nuclei, actually result in fusion. Too much helium in the mix or anything else and fusion rate will decelerate. From time to time it may be that helium, the waste product, needs to be cycled out of the core. But this can only happen if the production rate declines. That is, less fusion and less solar activity."

But like Dr. Boyle she believes it should be a temporary event. "Eventually the surplus helium is cycled out of the core and fusion returns to its former rate." For how long? "A few years, I think. We don't know for sure. The calculation is difficult." Dr. Sunshine has asked for two of the neutrino experiments to resume measurement of the solar neutrino flux, but to no avail. "This would give us a direct view of what is going on in the core right now. They're just not convinced that this is urgent."

Wandering off the mainstream there are more outlandish theories about what's going on. Outlandish, yes, but then so is the solar activity forecast. Perhaps among these mavericks the truth can be found.

A professor who uses his tenure as a shield against his critics to repeatedly push at the boundaries of science is Dr. Hernando Cojo. His hypothesis brings us face to face with one of the more profound and puzzling aspects of thermodynamics. The hydrogen atoms could, all at once, jump out of the core leaving only helium behind. "It's a rare thing but it's quite possible," he points out. "Thermal equilibrium is nothing more than the most probable arrangement of hydrogen nuclei. Think of it as the equivalent of that old joke about suffocating because all the air molecules simultaneously jump to the other side of the room."

Physicists we consulted dismissed his hypothesis: it's just too improbable, unlikely to happen over the lifetime of our solar system. But, Dr. Cojo claims, there are 8.9 × 10⁵⁶ hydrogen atoms in the sun and we only need a small fraction to do this. "That's a lot of material and improbable states are happening all the time somewhere in the sun. And keep in mind there may be 10²⁴ stars in the universe, and vastly more than this in some versions of cosmic inflation. The universe is big, really big. It's nearly a certainty that it will happen somewhere. So why not here, now!"

He likens it to a lottery. Your chance of winning is minuscule, as is everyone else's. Leaning forward he emphasizes the point with some heat. "Yet, someone does win."

A more peculiar proposal comes courtesy of Dr. Constance Boltzmann. Hydrogen in the core exists as a plasma, having been stripped of its electrons. She asks questions about those missing electrons. "It's a plasma because the high energy conditions prevent electrons from binding to protons. But the electrons have to go somewhere. They aren't lost."

In her theory the heat of the fusion furnace pushes them to the periphery of the core where they form a layer of highly negative charge. The core, full of hydrogen and helium nuclei, is positively charged. "It is sustainable for awhile," she claims, "but eventually something has to give." That something is what she coolly refers to as the mother of all lightning strikes. "The plasma fractures and the electrons rejoin the protons."

The charge neutralization is brief since the core is too hot and the electrons are stripped out again. This takes time. "Until then fusion is reduced because the electron partial pressure increases the distance between hydrogen nuclei. It's probably what caused the Maunder Minimum. The core goes through these cycles, but an irregular one that is difficult to forecast."

Drs. Sunshine and Boyle, at least, have submitted papers to high profile scientific journals for peer review in an attempt to reach out to the broader astrophysics community. More minds on this important problem should bring us closer to the truth. It might also serve to free up resources to gather data, such as the solar neutrino flux that Dr. Sunshine is so keen on. Time will tell.

There have been more alarming theories proposed than the ones presented in this article. We have chosen to leave those aside for now because they are indeed quite worrisome. We can hope that NOAA's ghastly solar activity forecast is mistaken and that cooler heads will prevail. Many of the experts we consulted for this article do not think that the worst is likely to come to pass. We can only wait for NOAA to issue their next forecast and hope for the best.

Don't worry and have a happy April 1^st.