Wake up! During the last solar minimum, the sun remained blank for many months at a time. Is this only the beginning? (NASA)
What if the sun’s magnetic field weakened so much that it wasn’t able to muster the strength to produce a single sunspot?
This scenario may sound a little odd, but according to researchers at the National Solar Observatory (NSO) in Tucson, Arizona, the sun is exhibiting a strange decline in magnetic strength, the driving factor behind sunspot production.
It’s as if our nearest star is getting tired and wants to take a breather.
Observing the sun since 1990, solar astronomers Matthew Penn and William Livingston have been diligently measuring the spectra of sunspots. By studying a sunspot’s radiation, a measure of the magnetism it contains can be derived.
Sunspots are locations on the solar surface (the photosphere) where magnetic field lines are forced from the solar interior. As these magnetic “tubes” bundle together, they push the hotter surface layer of the sun aside exposing the cooler (and darker) interior.
The result is a contrasting dark spot where the solar interior is exposed, held open by the upwelling of magnetism. Small sunspots are descriptively known as “pores.”
Sunspots most frequently appear when the sun is at its most stressed state in its 11-year cycle. At “solar maximum,” the solar magnetic field is so stressed that huge loops of magnetic field lines pop up all over the surface, generating lots of sunspots. The current solar cycle (Solar Cycle 24) is set to peak around 2013.
By analyzing a sunspot’s spectra, we are able to see the light emitted from specific elements that are present. Each element produces its own frequency of radiation that shows up as a spike (or “emission line”) in the spectrum.
Penn and Livingston have been taking a very close look at an emission line generated by a particular iron isotope. Using highly sensitive equipment at Kitt Peak McMath-Pierce telescope, this line appears to split, caused by extreme magnetism inside the spot.
This well-known phenomenon is known as “Zeeman splitting,” and the amount of splitting can be used to measure the strength of the powerful magnetic field inside a sunspot.
After notching up two decades of magnetic data from using this method, the solar researchers have noticed a startling trend. The solar magnetic field strength is decreasing. Rapidly.
“This trend was seen to continue in observations of the first sunspots of the new solar Cycle 24, and extrapolating a linear fit to this trend would lead to only half the number of spots in Cycle 24 compared to Cycle 23, and imply virtually no sunspots in Cycle 25,” Penn and Livingston say in their paper submitted to the International Astronomical Union Symposium No. 273 (emphasis added).
Since they started taking results, the researchers have noticed an average magnetic field strength decrease of 50 Gauss per year (as a comparison, the Earth’s magnetic field barely measures in at 1 Gauss).
“…we assume that the magnetic threshold of 1500 Gauss represents a real physical
limit for the formation of a dark spot (either a pore or a sunspot) on the solar photosphere,” they add.
If the decreasing trend continues its downward slope, by 2016, the average sunspot magnetic field has the potential to be below this 1500 Gauss threshold, leading to the possibility that the sun will generate no sunspots.
The last time this happened in documented history was in the 17th and 18th century when the sun didn’t produce any sunspots for decades. This extended period of calm, known as the Maunder Minimum, coincided with an extended period of cooling on Earth, a period called the Little Ice Age.
Are we witnessing another slow-down in solar magnetic activity? Could this be a part of a long-period cycle where the sun runs out of juice and forgets to produce sunspots every few hundred years?
I’ve been following Penn and Livingston’s research for some time, and it is fascinating to say the least. Although they are the first to admit their work is far from conclusive — two decades-worth of solar data isn’t a lot after all — this downward trend in magnetic field strength is a conundrum.
Although the sun is our nearest star, it certainly isn’t ready to give away many clues as to how it works quite yet.