Why Solar Nanoflares Matter

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The mystery of the solar corona may be resolved. ScientificBlogging has covered this, as did space.com, Space Fellowship, and other sites. Two of them couldn't resist the same money quote, too:

"Why is the sun's corona so darned hot?" said study member

James Klimchuk of NASA's Goddard Space Flight Center in Greenbelt, MD.

Why is this useful?

To recap the problem, the outer atmosphere (corona) of the sun is millions of degrees, while the surface of the son is merely thousands of degrees. So something mysterious between the nuclear fusion of the sun's bulk and the nearly invisible, wispy outer shell of gas is going on.

It can't be just heat flowing out of the sun, because heat flows from hot to cold, not cold to hot. The two big theories were 'wave heating'and 'reconnection'. For wave heating, sound or radio waves from the sun's surface travel to the corona then dissipate into shock waves, dumping energy into the corona. Depending on the wave's frequency and which detectors we have, we can see these waves.

Reconnection says that magnetic loops arc over the sun's surface into the corona and back down. The loops can carry heat from the surface to the corona, and their breaking and reforming can dump energy into the corona. As it happens, magnetic reconnection also causes flaring-- so it can be observed.

The flaws with both theories were that we didn't see the predicted behavior happening. Both make observational predictions, that we just didn't see. We've seen transient waves, but not enough to power the uniform coronal temperatures we see. We see large and small flare events, but again, not enough to drive the coronal temperatures seen.

One solution put forth to solve the "can't see it" part of the reconnection theory was postulating there were lots of microflaresdumping the energy -- flares we couldn't see. So we launched better instruments and, hey, not enough microflaring to deliver.

The next step is to suggest nano-flares. Now, this being science, you can't just say "okay, maybe something smaller than microflares", just because you like the idea. You have to have a reason. Klimchuk (among others) did modeling and simulation work that suggested that nanoflares could exist in the Sun. By modeling, they were able to set observational limits on how visible they were.

And so the recent result is that the nanoflares predicted were observed. They observed the footprints of likely nanoflares in active regions. The idea is (if I grasp it properly), if you see an tiny part of a magnetically active region on the solar surface with surprising million-degree temperatures, and you have a million-degree corona, then you can assume a connection.

As always, this one result isn't the end-all-be-all of the sun. For example, here's an explanatory cartoon from a 2008 paper "Coupling from the photosphere to the chromosphere and the corona" (Wedemeyer et al):

Coupling from the photosphere to the chromosphere and the corona

CLICK FOR FULL SIZE.

Okay, the sun's complex. I get it. I'm still psyched about the nanoflares observation, because you can see the result in two different ways:

active regions -> nanoflares -> heats corona -> hot spots at footprints (observed!)

Or...

theory -> model -> observation -> (not seen) -> revision of theory -> model -> observation -> seen!

Science for the Win!

Alex, the Daytime Astronomer

The Daytime Astronomer, Tues&Fri here, via RSS feed, and twitter @skyday

Comments

I would have rationed that although the sun is a fusion reactor, as the photons and hydrogen atoms are ejected during micro flares, these particles collide and create micro fission reactions, thereby creating incredible temps!
I would also think that the light, sound, and magnetic waves would contain so much energy, that if they collided this could create intense heat. Lasty, the flares have to create intense static build up. This would discharge and cause a surge in temp. I would liken it to lightening here on earth, which I think is millions of degrees, or at least the air around it.

Mind Master JD (not verified) | 08/18/09 | 23:15 PM

Hi MM JD,

You're mostly on it-- you talk of light, sound and magnetic waves carrying energy, that's the wave explanation. The flares do have an electrical (magnetic) component that delivers energy, that's what we call magnetic reconnection. The idea of micro fission reactions is slightly off-- the photons and hydrogen atoms do collide and generate energy through the usual colliding bit, it just isn't fission. But indeed, all 3 processes-- waves, recombination, and collisions-- do occur.

And the lightning analogy is pretty useful (useful enough I may steal it!)-- just as lightning heats the air near it to millions of degrees, so do magnetic reconnection events heat the corona. But our air isn't uniformly a million degrees everywhere-- we don't get enough lightning to heat all of our atmosphere. And similarly, the problem with saying 'flares heat the corona' is that there weren't enough flares observed to heat the entire thing, yet for some reason we still see the corona millions of degrees everywhere.

The sticky issues is how much of each heating method occurs, based on what we see, and is what we see enough to justify the temperature of the corona we measure. The nice thing about the recent nanoflares work is it says, aha, we see lots of little flares going on, so the flare contribution could be enough to explain the temperatures we see everywhere in the corona.

In the end, science comes down to observables-- no theory can survive if it can't be observed. That's the part I find neat-- that in the end, all the thinking in the world still has to yield to reality :)

Alex Antunes | 08/19/09 | 09:32 AM

Oh my, now you have my wheels turning. What about the sum of the three processes? I know you have calculated the mass of the substances used to induce the corona temps at various levels, and for that matter the energy (cycles) in the waves. It's been proven that energy is mass times the speed of light ^2 so there has to be something major going on in the Corona. The article also mentions the temp levels on the sun's surface being much less.

Do you use Spectrophotometer to determine the composition throughout the levels, and thereby quantify the mass of all these areas by atomic weight, and then it all has to balance right? If my perception serves me correctly, I think if you add up all three processes, you are still coming up way short on energy/mass/waves to get those types of temps.

I am just using my logic here, but I would think one would find the hottest temp in any reaction in the core. Evidently, there must be two types of reactions going on. If the masses are equal doesn't this provide mathematical proof via a simple equation of why it so hot in the corona? The unknown variable has to have a value, you just don't know what the variable is, and if it is comprised of the three processes, what the ratio of each is to the total energy.

In addition, with the coronal temps so high, doesn't this create plasma? What about particle reactions and behavior through this medium? Do we absolutely have the physics of all particles in all types of mass? I know a few of the heaviest elements exist for very fleeting periods. There might be an element that we don't even know about. In fact, we have made a few elements here on earth, but then again, maybe there is nothing new under the sun, or in this case around the sun. Have you considered using the heaviest of particles in the elements for your equation?

Lastly, I know you said there are no fusion reactions, but particles traveling at the speed of light, or faster, then colliding, release tremendous amounts of energy, which have to at least create micro black holes, which are very dense. The prevalence of these collisions could be so significant it may give off the illusion of all the light coming from the sun, but it might not be the total picture.

Again, as you know, mass is energy, and dark matter is more populous in the universe than the matter we can account for, so could dark matter be fueling the extreme temps in the Corona? The energy has to be coming from somewhere!

Maybe the light and temps coming from the corona are not totally surface related at all. Could it be that micro-massive black holes, created as a direct result of photon collisions which create cosmic energy rays 100 million times more energetic than anything produced by the most powerful particle smashers on Earth, and are even more energetic than the rays from an exploding star, might be responsible for the corona temps? The frequency of these types of micro-massive black holes should be tremendous right?

Could this be the answer?

MM JD (not verified) | 08/19/09 | 16:44 PM

Hi,

Short answer is: yes, it is indeed plasma, which does behave oddly and makes for complicated situations. There aren't any faster than light particles and not many high-speed (relativistic) ones, and what there are we can account for. So no micro black holes. The sun's energetic compared to stuff on Earth, but it's not really at science-fiction-inducing levels that would be needed for ultra high energy cosmic rays (or micro black holes) to be relevant. And as far as dark matter, well, I try to avoid that stuff myself :) As currently parameterized, dark matter would not explain it either.

The significance of Klimchuk's nanoflares work is he really did seem to spot the cause. The cause is constant nanaflaring on the Sun, which required the Hinode instrument to finally spot, and which seem to be abundant enough to provide the missing heating. So I'll go with Occam's Razor and say he may have solved it, with a simple yet elegant solution.

However, if it is due to dark matter inducing micro black holes, I'll be first on record of saying 'whoops'. (That's a joke, btw... if dark matter induced micro black holes that frequently, we'd see them evaporate via Hawking radiation).

Alex Antunes | 08/19/09 | 16:56 PM

Thanks, please just three more questions on this subject because I am very curious,

If the research seems to support nanoflares, and the subsequent reconnections as the culprit for the temps, how is the corona so evenly distributed and uniform in temp, or does it just appear to be like this? Would it be from simple diffusion if it were?

Can the Corona be compared to our atmosphere? If so, why is it that our atmosphere generally contains the same amount of mass, and like you said, it is not millions of degrees as a result of lightening? Nevertheless, we can predict the weather with regular frequency, but not lightening.

The flares just seem so random to me, even the nano flares, just like lightening, and in a sense so chaotic, that the collisions of the particles would be way more reliable as far contributing to cause of the temps which seem to occur with regular predictability. The sun expels a certain amount of particles regularly, so much so that our survival is based up this fact. Big flares send out powerful waves, but these do not happen regularly, and they can not be predicted. The energy coming from the sun can, just like an atomic clock and carbon dating. I'm going to try and paraphrase what I said by simply stating that how could something so random contribute to something so regular? Here are my most important questions:

1. Because there is no unified theory between astro and particle physics, could the three types of black holes, micro, regular, and super-massive, release different types of radiation? Is this radiation EMR in all instances? Is magnetic reconnection radiation EMR?

2. Would it be possible that the micro black holes' radiation is harder to detect because of its’ size and fleeting existence it there were present in greater numbers?

3. Lastly, I learned in regular high school physics, which is primarily Newtonian based, that the speed of two particles when they collide is summed to quantify the total energy. Why doesn't this apply to the photons coming out of the flares when they collide, thereby making them almost as fast as the speed of light, or at least relativistic?

Thanks again!

MM JD (not verified) | 08/20/09 | 13:13 PM

Hello, this is just a correct version of what I wrote above. It, probably seemed a little crazy how I wrote it because I did it so fast, but hopefully you will better understand my questions now.

Thanks, please just three more questions on this subject because I am very curious,

If the research seems to support nanoflares, and the subsequent reconnections as the culprit for the temps, how is the corona so evenly distributed and uniform in temp, or does it just appear to be like this? If it is uniform in temp, would it be from simple diffusion from the nano flares if it is?

Can the sun's corona be compared to our atmosphere? If so, why is it that our atmosphere generally contains a constant amount of mass, and like you said, it is not millions of degrees as a result of lightening? Nevertheless, we can predict the weather with regular frequency, but not lightening. Seemingly, the lightening is insignificant in the total constant temp of our atmosphere.

The flares just seem so random to me, even the nano flares, just like lightening, and in a sense so chaotic that the collisions of the particles would be way more reliable as far contributing to cause of the temps which seem to occur with regular predictability.

The sun expels a certain amount of particles regularly, so much so that our survival is based up this fact. Big flares send out powerful waves, but these do not happen regularly, and they can not be predicted. The energy coming from the sun can, just like an atomic clock and carbon dating. I'm going to try and paraphrase what I said by simply stating that how could something so random contribute to something so regular? Here are my most important questions:

1. Because there is no unified theory between astro and particle physics, could the three types of black holes, micro, regular, and super-massive, release different types of radiation? I know the quantity would be grossly different. Is this radiation EMR in all instances? Is magnetic reconnection radiation EMR?

2. Would it be possible that the micro black holes' radiation is harder to detect because of its’ size and fleeting existence it they were present in greater numbers?

3. Lastly, I learned in regular high school physics, which is primarily Newtonian based, that the speed of two particles when they collide is summed to quantify the total energy. Why doesn't this apply to the photons coming out of the flares when they collide, thereby making them almost as fast as the speed of light, or at least relativistic? Would these collisions release energy commensurate with fission reactions? I think you are stating that fission reactions would be difficult because of the bonds and stability of the hydrogen atom right? But you also mentioned that particles behaved oddly in plasma, and I've never read anything with regards to the behavior of bonds in plasma.

thanks,

Joe

Thanks again!

Anonymous (not verified) | 08/22/09 | 14:22 PM

Okay, let me tackle at least some of this.

> If it is uniform in temp, would it be from simple diffusion from the nano flares if it is?

Yes.

> Can the sun's corona be compared to our atmosphere?

No. Simplifying greatly (because both are pretty darn complex), the solar corona is a rarefied plasma with an enormous heat source below it that also has strong magnetic fields moving through it. Our atmosphere is a relatively dense gaseous body with little global magnetic interaction to worry about. So we have to use plasma physics and magnetohydrodynamics for the corona rather than the statistical thermal physics we use for our atmosphere.

> The flares just seem so random to me, even the nano flares

The concept is they are frequent. Random is fine as long as they are frequent, so you get a continuous total output. Our sun is an active star, so there's a lot going on-- the earlier models of it being primarily a stable thermal source were blown away by the early Yokkoh and other results, and we now understand it's very complex.

Historically, Yokkoh thought 'hey, we take a picture a day, we're fine', then found out woah, we need a much higher cadence (number of frames taken per day) to get interesting results. SOHO had a higher cadence, and HINODE has instruments that take more rapid frames than that, and we still don't capture all that happens.

> The sun expels a certain amount of particles regularly, so much so that
our survival is based up this fact.

Not to be contrary, I would argue our survival is in spite of the particles being spit out (fortunately our Earth's atmosphere shields us greatly).

> The
energy coming from the sun can, just like an atomic clock and carbon
dating.

Eh, not quite. Besides the overall solar cycle, different solar cycles have different outputs. It turns out the total irradiance of the sun is an interesting field unto itself.

> 1. Because there is no unified theory between astro and particle
physics

Actually, astronomy does use physics, there is no disparity. What astronomy does it let us measure physics in the very big or very hot range, while particle physics experiments let us measure things are the very small range. But it's all the same physics.

> could the three types of black holes, micro, regular, and super-massive, release different types of radiation?

Nope, it's all still basic physics at work: gravity, light, energy.

> 3. Lastly, I learned in regular high school physics, which is primarily Newtonian based, that the speed of two particles when they collide is summed to quantify the total energy. Why doesn't this apply to the photons coming out of the flares when they collide, thereby making them almost as fast as the speed of light, or at least relativistic?

Photons and particles are different. Photons already travel at the speed of light, always. Photons can interfer (their wave-like property) but they don't collide per se. Typically, a photon will interact with a particle and there will be a transfer of energy, which changes the wavelength of the photon (but not its speed) and the energy of the particle (either its speed or, if talking about electrons around atoms, its energy state).

So, at the risk of overstating things, 1) the Sun obeys conventional physics, as do black holes, 2) plasmas have unusual but well understood (to a plasma physicist) behavior, particularly regarding magnetic fields, 3) the sun is an active star, 4) the Klimchuk nanoflare model would have enough activity to drive the coronal temperatures involved if such nanoflares exist, and 5) the model was validated when observations revealed the presence of sufficient active nanoflaring sites (that had not been seen in earlier observations because they required the high fidelity detectors of Hinode to be seen.)

I hope that clarifies!

Alex Antunes | 08/22/09 | 22:21 PM

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