I learned this today. The sun flips its magnetic field and its north south poles once every 11 years because its inner dynamo reorganizes itself.
How does the sun get its magnetic field? The sun is made of hydrogen and helium gas. Inside the sun, the immense pressure turns that gas into a plasma. Plasma is the fourth state of matter, the others are solid, liquid, and gas. Plasma is formed when gas is superheated to such a degree that the electrons are torn away from the atoms. When the electrons are removed, it leaves the charged atoms, called ions, and the electrons float freely. The ions are left with a positive charge, and the electrons have a negative charge. When this plasma moves around inside the sun, the charged particles create a magnetic field. This is known as the solar dynamo. The plasma creates a magnetic field, but the magnetic field then controls the movement of the plasma, so they are dependent on each other.
The plasma and the charged particles move about the sun in different ways and create different magnetic fields. There is the electric field that surrounds the sun, which is twisted because the plasma moves so much. There is also the hot plasma that streams off the sun as solar wind, which also causes a magnetic field. The plasma moves faster at the sun’s equator than it does at the poles, so the magnetic field gets stretched and twisted. All of these different things combine to make the sun’s overall magnetic field.
The sun’s magnetic field is enormous and is carried into space on the solar wind. This is a stream of charged particles that flow outward from the sun, through the solar system. This magnetic field is called the heliosphere and the boundary of it separates the solar system from interstellar space. That boundary is about 16,950,000,000 km from the sun and Voyagers 1 and 2 have both crossed it.
The dynamo within our sun creates its magnetic field because of the way the plasma moves inside it. All stars produce a magnetic field in the same way and the strength of that field depends on the rotation of the star, and the convection that causes the plasma to rise and fall within the star. And the dynamo also makes the sun’s poles reverse every eleven years.
This is not unusual, and the poles of all planets with a magnetic field reverse regularly. Our poles on Earth reverse every 300,000 years on average, although the last time they reversed was 780,000 years ago. The solid iron core at the center of our planet is surrounded by an ocean of liquid metal. This interaction between the two bodies creates our magnetic field and also means that our dynamo is not static. It moves and the poles of the magnetic field move with it. When the core flips over, the poles flip over.
The sun is no different. The plasma inside it that creates its magnetic field moves and the poles of the magnetic field move with it. The only difference between the sun and Earth is that the sun takes 11 years to do what we do in 300,000.
Why is it 11 years? Nobody knows, but it has a connection to the size of the sun and how quickly it rotates. As I mentioned earlier, the plasma at the equator rotates faster than that at the poles. This drags and stretches the magnetic field as the center bit goes faster than the edges. The equator makes a complete rotation every 27 days, and the poles take 34 days. This gradually wraps the magnetic field lines around the equator. The field becomes stronger and stronger until it reaches its maximum and it modifies the gas pressure equilibrium in the surface layer of the sun, making magnetic field lines come up Where they break the surface, they cause sunspots. Once the magnetic field has become as wrapped up as it possibly can, it has reached its maximum and it starts to decline. Once this happens, the natural currents in the surface of the sun start to pull the field lines toward the poles. They gradually pull the field lines away from the equator and the poles reverse. By this time, the field lines have started to wrap around the equator of the sun again and the whole process repeats itself. This process takes an average of 11 years. This has an effect on us here on Earth because the increased sunspots and solar storms can mess with technology and alter weather patterns.
So, the sun’s poles rotate every 11 years because the dynamo within the sun moves and the magnetic field rotates more quickly at the equator of the sun than it does at the poles. And this is what I learned today.
Photo by Pixabay: https://www.pexels.com/photo/sun-fire-hot-research-87611/
Sources:
https://scijinks.gov/solar-cycle/
https://en.wikipedia.org/wiki/Solar_cycle
https://scied.ucar.edu/learning-zone/sun-space-weather/sunspot-cycle
http://ibex.swri.edu/students/How_does_the_Sun.shtml
https://www.nasa.gov/feature/goddard/2016/understanding-the-magnetic-sun
https://www.psfc.mit.edu/vision/what_is_plasma
https://www.windows2universe.org/sun/sun_magnetic_field.html
https://en.wikipedia.org/wiki/Solar_wind
https://en.wikipedia.org/wiki/Heliosphere
https://www.nasa.gov/content/goddard/the-suns-magnetic-field-is-about-to-flip/
https://www.nasa.gov/topics/earth/features/2012-poleReversal.html