30 July 2019

Sun Churn

Sun Churn G. Petrie/NSO/AURA/NSF

In addition to heat and light, our sun cranks out a complex, swirling magnetic field.

Story by KRISTIN ROBERTS and CLAIRE RAFTERY

Measuring Magnets

Here's how the sun's field stacks up with other magnets in the solar system as measured in teslas, a unit of magnetic field strength.

Earth 0.00005 tesla
Sun 0.0001 tesla
Fridge magnet 0.01 tesla
Sunspot 0.4 tesla
Junkyard magnet 1 tesla
Hospital MRI 1.5 – 3 teslas
Strongest MRI for animal research* 21.1 teslas
Strongest continuous-field magnet used in research* 45 teslas

* Located at the National MagLab

For this field trip, we're travelling 93 million miles to shine a light on the sun's magnetic field, a complex phenomenon that a powerful new telescope will soon help us better understand.

Similar to our own planet, the sun is like a huge bar magnet with a north and a south pole producing a magnetic field. But the sun's magnetic field is about twice as strong as the Earth's and much, much larger, extending well beyond the farthest planet in the solar system.

The sun's field is also a jumbled mess. As the sun rotates, the plasma near the poles rotates more slowly than the plasma near the equator. This off-rhythm spinning causes the magnetic field to get twisted and tangled into massive bundles. As the fields get more and more tangled, they burst through the sun's surface, leaving marks we know as sunspots. Around a sunspot, the magnetic field can reach as high as 0.4 tesla, which is around 4,000 times stronger than the field at the sun's poles, but more than 100 times weaker than the massive electromagnets at the National High Magnetic Field Laboratory (see sidebar).

If that's hard to envision, the above image from the National Science Foundation's National Solar Observatory Integrated Synoptic Program can help you out. The program has taken daily images of the sun's splotchy magnetic field for more than 40 years and uses them to create a model of the magnetic field in the sun's outer atmosphere, called the corona. In the picture above, the bright solar disk, which is more than a million times brighter than the sun's outer atmosphere, is blocked out and the modeled magnetic field lines are traced. Solar wind blows outward along the open magnetic field lines (traced in yellow), while the closed field lines (in teal) that loop back onto the sun trap plasma in planet-sized arches called coronal loops.

The sun's magnetic fields get jolted around by constantly bubbling surface gases; when they come in contact with each other, they create a short-circuit-like effect called magnetic reconnection. Short-circuiting the magnetic field over and over helps the field unwind itself over time, an 11-year process known as the solar cycle. Over the course of that cycle, the number and location of sunspots varies, which help scientists predict space weather.

Today, the best scientists can do is use models to understand the magnetic field in the corona. However, the NSF is building what will be the world's most powerful solar telescope, the Daniel K. Inouye Solar Telescope, in Maui. When it comes online later this year, researchers will be able to measure magnetic fields in the corona for the very first time.

Last modified on 12 August 2019