The Sciences

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

Bad AstronomyBy Phil PlaitAug 19, 2011 10:00 AM


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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.

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[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

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