The sun’s giant heat elevators
COURTESY OF D. HATHAWAY/NASA
Going up! In the sun, heat rises from its scorching interior to the surface, carried by plumes of solar material. Neither solid, liquid nor gas, these plumes are made from plasma — a fourth state of matter. Scientists had known these plumes could be huge. Now astronomers have found mega-plumes. They are bigger than any measured before and much longer-lived.
Their existence also may explain why the sun rotates more quickly around its “waistline” than at its poles.
Close-up pictures of the sunshow the tops of these plasma plumes. Astronomers call them granules. Each looks like a little grain. All together, they resemble a mosaic made from puzzle pieces. Each granule may be about 1,000 kilometers (621 miles) across and last for about 10 minutes. Even bigger ones, called supergranules, can be as wide as Earth’s diameter and last for a whole day.
But for decades, researchers have suspected that plumes come in an even bigger size. Now, a team of astronomers says they’ve found the first evidence of these. In the Dec. 6 Science, David Hathaway and his coworkers describe observing plumes more than 15 times as wide as Earth’s diameter. And these mega-plumes are persistent: They can last months.
Hathaway is a solar scientist at NASA’s Marshall Space Flight Center in Huntsville, Ala. His team studied data collected by the Solar Dynamics Observatory. This spacecraft studies the sun using powerful tools. One measures the color of the sunlight in relatively small patches of the sun’s surface. By studying these data, astronomers have computed the speed and direction of moving mega granules. They’ve now shown that these mega-plumes are pushing fast-rotating plasma toward the sun’s equator and shoving slower-moving plasma toward the poles.
Mapping these mega-plumes isn’t just important for understanding heat transfer on the sun. It also helps answer a question that has vexed scientists for centuries: Why does the sun rotate faster at its equator than at its poles? Calculations had suggested this should be impossible — unless a huge upwelling of plasma gave an added boost to the circulation of matter around the sun’s middle.
Mark Miesch is an astrophysicist at the National Center for Atmospheric Research in Boulder, Colo., who did not work on the study. He uses computer programs to model, or simulate, the sun’s heat flows. The new study delivers good evidence for mega-plumes, he told Science News. Still, the findings don’t mesh perfectly with those from previous studies. So while he thinks the new study is promising, he “wouldn’t call it a slam dunk.”
astrophysics An area of astronomy that deals with understanding the physical nature of stars and other objects in space.
granule A cell on the surface of the sun that has temperatures a few hundred degrees hotter than the surrounding regions and lasts a few minutes.
model A simulation of a real-world event that’s developed to predict an outcome.
plasma A state of matter in which atoms start to come apart, with the electrons leaving behind the nuclei to which they had been bound.
solar Having to do with the sun, including the light and energy it gives off.