The Sun and its Danger Zone: The Chromosphere

One of the deeply confusing aspects of our Sun (and other stars) is their temperature structure. Starting in the core, the Sun is millions of degrees kelvin and supports nuclear burning. As you leave the nuclear burning core and climb first into the radiative zone and then the convective zone, the temperature systematically drops until it reaches a temperature of several 1000 degrees at a star’s surface. This makes sense. In the core, the gas is being compressed under the pressure of all the upper layers of the star gravitationally pushing down. The pressure allows nuclear reactions to release energy in a form that can heat things up: specifically light. That light then interacts with stellar material, being absorbed and reabsorbed over and over as it loses energy and goes on a random walk through the radiative region (think light bulb heating the air around it), and then (think of the lava lamp material above a light bulb) it also gives off energy as it heats cells of material at the base of the convective zone that rise and convectively give off heat as the cells rise (and then, when cool, sink back down).

So far so good.

The problem is, as you then move away from the surface of the Sun, you enter regions where the temperatures again go up – A lot – like back to millions of degrees hot levels of a lot!

And no one fully knows why. This is a very counter intuitive situation. Imagine that the surface of a lava lamp was 23C and the air half an inch away was 200C! In a press conference Wednesday, astronomers announced that they think they may have found a starting point for understanding what is going on in this bizarre situation.

In a pair of presentations given by Bart De Pontieu (Lockhead Martin Solar and Astrophysics Laboratory) and Scott McIntosh (Southwest Research Institute) it was shown that a combination of sound waves and magnetic fields can channel energy (and heat is a form of energy) into the Sun’s Chromosphere. In their models, they find that sound waves propagate through the convection zone, and the energy within the sound waves can escape in locations where broken magnetic field lines form solar spicules (a time of flame shaped thing). The sound waves trigger shocks that super heat fountains of material that is ejected into the chromosphere. When they compared their models to actual high-speed images they found excellent correspondence between modeled expectations and reality.

During the press conference’s questions session, one of the journalists asked, (to paraphrase), “Why should we think that 10 years from now we’ll be saying that the question of ‘Why is the Chromosphere so hot’ was definitively answered in 2007?” While that may sound like a really obnoxious question for a generally well-behaved room full of science writers, it was actually a really honest question. We still don’t fully understand the Sun’s magnetic field or exactly what causes the field lines to break and reconnect is a bit hairy to try and understand and model. We still don’t fully understand how convection works in the Sun either. We are incrementally building better and better tools for modeling what we observe, but our theoretical models include lots of assumptions. To say we can definitively announce anything that includes both magnetic fields and convection is, um, optimistic.

But this is a start. I honestly think that 10 years from now, as we continue to build a fully refined understanding of what is going on, the papers written on the results shown in this press conference will be cited. Tomorrow’s understanding builds on yesterdays results. Sometimes science goes in leaps of ingenuity. This is not one of those times, but it is still solid science.

Next Up: Tidal Streams…

3 Comments

  1. Louis R. Liberatore June 4, 2007 at 9:00 am #

    Dr. Gay,
    I couldn’t find your email so I’m trying this. Never blogged in my life but after reading your S&T 6/07 review thought I should try contacting you. By the way, my older daughter insisted on getting me a B-Day present and I suggested “Life As We Do Not Know It” based upon your review. My older daughter should be getting her doctorate this summer (Molecular Biology, Columbia Univ, did her undergrad at Princeton). This book combines a little of her interests and my hobby of astronomy. The following is something that I’m pursuing and I would greatly appreciate your comment. >>> I’m looking for a source where I might obtain information or opinion on the potential for distortions/ warping in space time in the early universe. Please allow me to explain.
    As you are aware, in the search for Dark Matter, there are many theoretical proposals of exotic particles to claim the position of the missing matter. As yet, none have been detected. There is also the MOND theory (modified Newtonian gravity). However, several months ago an alternative occurred to me that I have not heard about. It does not require changing the laws of gravity nor finding exotic particles. It made so much sense that I figured I must have made an obvious error. A friend of mine who is a professor of physics informed me that he couldn’t find anything wrong with it and that it was the most reasonable solution he had heard. As you will see, it is after all, an Occam’s Razor approach. Frankly, it is so “clean” an alternative, I believe it deserves a closer look.
    As I understand it, gravity is best interpreted as a distortion in space time. Even Hawking concedes that gravity is geometry and quantum will have to incorporate some form of it. It seemed quite plausible to me that the proper distortion/ geometry of space time should produce gravity without the need for matter. I’ve since received an opinion from a notable astrophysicist that THERE CAN BE GRAVITY WITHOUT MATTER. With this encouraging and authoritative opinion in hand; I’ve been pursuing the following alternative. What do we really know about Dark Matter? We know there is a lot of gravity but we have not detected the matter associated with this gravity. With the possibility that there can be gravity without matter; I believe it begged the following question. WHAT IF THERE IS NO MATTER IN DARK MATTER (DM)? The astrophysicist then suggested that I prove my idea that what I’ve labeled Matter Less Gravity (MLG) is the source of DM. To this date, no professional or amateur that I’ve contacted has yet to discover or mention a flaw with my idea.
    My problem is that it is extremely rare to receive any opinion. I don’t know if that is a result of my being an amateur; I’ve contacted the wrong people about this subject or is it because it’s viewed as too dumb to deserve more of a response. The few responses I received suggest it is not a dumb idea.
    Given that we already have well established observations of vast amounts of gravity and no detectable associated matter: it appears that my next step is to inquire how substantial quantities of Matter Less Gravity could be generated. My feeling is that I should be looking at the very early universe. The conditions of that time period might be conducive to generating the distortions/ geometry of MLG. Also, if we are talking about the inflationary time period, it may be likely that the homogeneous distribution of MLG provided the framework, the “skeleton” for which the baryonic matter would be attracted and attach itself to resemble the results as reported by WMAP. I suspect that a computer model could add credence to this suggestion. Any information, ideas or discovered flaws related to my alternative approach or even a suggestion as to whom I should contact would be greatly appreciated.
    Respectfully,
    Louis R. Liberatore
    Spring Glen, NY
    LouL@hvc.rr.com

  2. pamela June 4, 2007 at 6:36 pm #

    Hi Louis,

    There is a section on th BAUT Forum designed for discussing ideas like this one. Please post for discussion in Against the Mainstream.” There are main professionals and knowlegable individuals in that group who can help you identify strengths and weaknesses in your ideas, and help you figure out how to move forward.

    Cheers,
    Pamela

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