Scientists see sunspots forming 60,000 km below the Sun's surface!

By Phil Plait | August 19, 2011 6:00 am

Sometimes I hear astronomy news that is cool, and sometimes I hear news that’s very cool… and sometimes I hear news where my reaction is, "That’s freaking insane!"

The latest news: scientists have used data tracking sound waves inside the Sun to see sunspots forming 60,000 kilometers (36,000 miles) deep in the Sun’s interior, fully two days before the spots erupt onto the surface!

That’s freaking insane.

OK, first, the video, then, the explanation.

[Make sure to set the resolution to 720p or 1080p to get the full effect.]

I love the last few seconds of that video; the rotation of the Sun sweeping the towering loops of magnetically-influenced plasma around to the limb is simply stunning.

So how does this all work? Sound waves.

Basically, inside the Sun, hot plasma (gas stripped of one or more electrons) rises and cooler plasma sinks. As it moves, it generates turbulence. This in turn creates acoustic waves — sounds — that travel through the Sun. As these waves move through the solar interior, regions with different densities make them speed up or slow down. The physics of this is pretty well understood, so by mapping how long it takes a wave to move between two points, the density of the stuff between them can be measured.

On board the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) are instruments that can measure the changes in the solar surface as these sound waves move around. There is a vast amount of data — and I mean vast, millions of data points — but by careful analysis that included eliminating a lot of sources of noise, the scientists were able to watch the sound waves change speed as they passed through the volume of plasma below the Sun’s surface where sunspots were rising. They could detect this material 60,000 km deep — that’s nearly five times the diameter of the Earth! These nascent sunspots move upward at about 1000 – 2000 km/hr, faster than the speed of a jet airplane. At that speed, it takes about two days to rise to the surface… and presto, that’s what’s seen: the subsurface spot erupts through to the surface, where we can see them directly.

Sunspots are regions where the Sun’s magnetic field is particularly intense, and the plasma is affected by this magnetism. The looping magnetic fields are embedded in the plasma as it rises to the surface, and the field lines pierce the surface, forming gigantic arcs. The spots are associated with the bases of those loops, as you can see in the video.

There are vast energies stored in these loops, and if those field lines get tangled up, they can snap, releasing that energy as explosive solar flares or enormous coronal mass ejections. Both of these are events of monumental power, sometimes giving off 10% of the total energy of the Sun itself! They also can hurl billions of tons of subatomic particles toward the Earth at large fractions of the speed of light, affecting our power grid and satellites.

Obviously, having two more days advance warning on sunspot formation would be a Very Good Thing.

The scientists doing this work have done it successfully for four forming sunspots so far. The method appears to work pretty well, and I hope it can be refined and sped up to give us more warning. Last week I was visiting the Big Bear solar observatory to film an interview, and noticed that the spot that blew off several flares was moving off to the far side of the Sun, but there were several spots still marring the surface. One of them, Active Region 1263, blew its lid just days later. How cool would it be to know that was coming, days before the spot itself was even visible?

Image and video credit: SOHO/MDI, SOHO/HMI, the SOHO MDI and HMI teams, NASA/SOHO

Related posts:

A computer’s spot in the Sun (a must-see gorgeous image!)
A fiery angel erupts from the Sun
The birth of a sunspot cluster
Sun blows out another big one; expect aurorae tonight


Comments (32)

  1. CJSF

    Phil, I remember you describing a dream you had once where you were “flying” over the Sun’s surface. Your description left chill-bumps on my skin! Every time I stop to really think about what the Sun *is*, I just don’t know what to say, except, “that’s freaking insane!


  2. Phil – Have you considered maybe having a sticky thread where people can ask you things they’re wondering about that would take things off topic otherwise? I have lot of questions about astronomy in general and even though I’ve read on some of it on wikipedia, and other sites, some of it wasn’t really cleared up for me. I don’t have a specific question right now but often I do and it would be nice to have a place dedicated to that on your blog.


  3. Timmy

    This could also be useful tool to warn us of an impending Faeros attack!

  4. riverlaw

    Caffeen Man. I can’t help but think there are forums better suited for asking questions. For observing and more I know cloudy nights is great. If I were you I would look for a forum dedicated the type of question you have… I know that is not super easy but its not super hard either.

  5. joakod

    The sun is the coolest object in the solar system.

  6. There is a forum associated with this blog:

  7. Erik

    #1 CJSF or Phil – you don’t happen to have a link to that dream description, so you?

  8. It would be a bit odd that we might be able to predict Sunspots and Coronal Mass Ejections two days in advance, but still have no advanced warning of Earthquakes.

  9. Messier Tidy Upper

    Whoah! ūüėģ

    Seeing 60,000 leagues (well, ok, klicks) below the surface of our Sun!?

    Yes. That. Is. Impressive. 8)

    Sub-solar astrophysics?

    @5. joakod :“The sun is the coolest object in the solar system.”

    Nah, Sedna is. ūüėČ

  10. Jason Dick

    Very cool! Now all we need is a stargate and we’ll have a time machine!

    (For the uninitiated: )

  11. @ IMForeman:

    It would be a bit odd that we might be able to predict Sunspots and Coronal Mass Ejections two days in advance, but still have no advanced warning of Earthquakes.

    Why? Totally different processes.

  12. sjc345

    I’m amused that the advert that appeared on the video was offering me a “Commerical Solar System”. OK, the ‘Large Scale Solar PV Solutions for your Business’ underneath gave it away, but for a moment I did wonder just what I could buy there…

  13. Jason

    It is fascinating that we can analyze sound waves on the sun. I assume, if I understand correctly we are observing what are essentially seismic waves through visual observation of the sun’s surface?

    I know that a similar technique is done to do subsurface studies of the earth. But using seismographs and such.

  14. Das Boese

    To me the most amazing thing about this technique of using sound waves to take a peek under the Sun’s surface is that it also works on other stars!

    Not to the extent of seeing individual sunspots form, of course, but still good enough to give us clues what’s going on inside stars that are light years away.

  15. Thanks guys. Next time I have a question I’ll sign up one of those places. I’ve saved the links. Much appreciated!

  16. Regner Trampedach

    Thanks for the heads up, Phil! Nice post. But the link to the actual press release from Stanford could be a bit more explicit and have more prominence… :-)
    MTU @ 10: We have been doing sub-surface astrophysics for quite a while now, using “global” helioseismology where you can learn how things changes with depth in the Sun – all the way to the core (this post is concerned with “local” helioseismology where you learn about the full spatial structure but only to a certain depth – 60 Mm is deep, though, but compare that to the Suns 700 Mm radius). From global helioseismology we have learned about pressure ionization in dense plasmas (i.e., the Sun is not an ideal gas), that the electrons in the Sun’s core are not only degenerate, but relativisticly degenerate (to a very small but measurable degree) and that the equator in the convection zone (outer third of the Sun) rotates with a 25day 17hour period and slower, with a 38day 14hour period towards the poles. The non-convective inner 2/3 of the Sun rotate as a solid body (all the same period) with the convection zones rotation rate at 35 degree latitude. That was only a few (biased) highlights – there is so much more :-)
    Cheers, Regner

  17. Jason

    Phil, I love these kinds of posts.

    I admit we differ Wildly on most major philosophical and political points, I am continually fascinated and amazed by what we learn about the universe. Science Works …

  18. I’ma gonna go drink a Pan-Galactic Gargle Blaster to clear my mind now.
    Don’t expect me back soon…

  19. Jason

    @richard Wouldn’t it be cheaper to just use a gold bar wrapped in a slice of lemon?

  20. @kuhnigget You’re being a bit literal, I think. I say it’s odd because it seems a strange turn of events when we can predict the future behavior of an object 93 million miles away, but the ground beneath our feet remains stubbornly mysterious. I’m not saying that the process of detecting sunspots has any application to predicting Earthquakes, or implying there are similar processes at work, but I am saying is basically “Life’s funny, innit?”

  21. Regner Trampedach

    Jason @ 14: You know how spies can listen-in on conversations in another house by measuring the vibrations of the window by shining a laser on the window to measure the Doppler effect and feed that velocity into a microphone for easy listening.
    We do a similar thing with the Sun. For other stars, Kepler looks at how the total brigtness of the star changes (about 10 parts per million!) due to these sounds waves.
    Cheers, Regner

  22. Jason

    Regner @ 22 I don’t think they are measuring Doppler with the laser, bu in fact its simpler than that. the window vibrations move window and cause the the laser reflection to move across the receptor. this is translated back into sound. I saw a project to build a simple one for something like $30 worth of electronics, maybe even less now since laser diodes are so cheap.

    There may be some that use Doppler to get higher quality sound or greater sensitivity, but I would think it would require very precise electronics

  23. CJSF

    @#8 Eric:

    I have only been able to track down a reference Phil himself makes to it in an old “Bite Sized Astronomy” article on his old website. That article only mentions it in a sentence, but I swear I remember him writing more about it somewhere (the aforementioned article is a good read, too). But we all know how faulty memory can be! If Phil manages to squeeze in some comment reading here, he may be able to shed light on it.


  24. Brian Too

    OK, point of clarification needed here.

    These regions of plasma are rising because they are hotter than the surrounding plasma. Got it. However I’ve always read that sunspots appear black because they are cooler than the surrounding plasma! So what is going on that would cause the sunspots to lose their relatively hotter temperature?

    Is it because we are seeing the surface sunspots in comparison with the corona, which I’ve heard is super hot?

  25. Wzrd1

    They’re not measuring doppler with the laser, they’re watching the beam reflection being modulated in amplitude by the vibration of the glass from the sound inside the room.
    There are a number of quite trivial counters to that method of eavesdropping that are highly effective.

    That said, it’s WAY cool that solar seismology now is well enough understood to actually ascertain magnetic storms making their way to the surface.
    Imagine what they’ll figure out how to observe in a few more years!

    Regner @ 17, I must have missed that bit about relativisticly degenerate electrons. More reading for later on! :)

  26. Bee

    Sunquakes are cool!

    How did they eliminate the noise? There must be loads. I mean, that’s a giant ball of plasma. Do they look for correlations?

  27. don gisselbeck

    This should put the nail in the coffin of the iron sun claims.

  28. csrster

    Bee – One thing that helps with helioseismology is that the oscillations typically have very long lifetimes (compared to their period). This means that they have very narrow spectral peaks. Also there are an extremely large number of excited modes so you can average over them to eliminate noise.

    Brian Too: At the solar surface, heat is being transported by convection. The magnetic field in a sunspot is strong enough to suppress the convection and hence the heat transport. (Think of the magnetic field as being like powerful elastic bands attached to the solar plasma. This makes it difficult to stir up the plasma.)


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