Our Sun emits solar flares on a regular basis, but what would happen if it released a flare 100,000 times more powerful than the largest flare in recorded history? Could it destroy our power grid, irreversibly change life on Earth, or even strip the atmosphere from our planet? Let the fear-mongering begin! 

Superflares are in the news, and with it comes wild claims about their possible threat to human civilization. As with most hyped stories, they focus on just how powerful one could be, and how it might disrupt human civilization rather than the actual science, which is unfortunate because the science is pretty interesting.  It’s based on recent work that looked at the flare activity of more than 5,000 Sun-like stars. What they found was that stars where superflares occur tend to have stronger magnetic fields than stars where superflares are less likely. This correlation between superflares and magnetic field strength suggests that superflares are produced by a mechanism similar to regular solar flares.

From solar observations we know that solar flares occur when magnetic field lines near the Sun’s surface “snap” into realignment. The Sun actually rotates differentially, meaning that its equator rotates a bit faster than its poles. As a result, over time the magnetic field at its surface wraps around the Sun a bit. When the magnetic field is twisted up, it can realign quickly, producing a solar flare. For stars with stronger magnetic fields, the resulting realignment has a tendency to be more severe, and thus large solar flares (superflares) are more likely. This work shows that superflares are not a different phenomena, but are solar flares on a larger scale. They also found that superflares can occur on stars with magnetic field strengths similar to the Sun. While superflares are much more likely on stars with strong magnetic fields, the team found that about 10% of the superflares they observed occurred on stars with magnetic fields on par or weaker than that of our Sun. From their observations, they estimate that a superflare could occur on the Sun about once every thousand years or so.

That said, if such a superflare were to occur today it wouldn’t end civilization as we know it. There is some evidence in tree ring data that small superflares might have occurred in 775 and 993 AD, with little effect on human society. In our modern world solar flares do pose some risk to satellites and our electrical power grid, but we have ways of limiting their effect. In a bad-case scenario we might have some infrastructure to rebuild, but it wouldn’t be an extinction-level event.

So there’s no need to worry. Just keep calm and science on.

Paper: Christoffer Karoff, et al. Observational evidence for enhanced magnetic activity of superflare stars. Nature Communications 7, Article number: 11058, doi:10.1038/ncomms11058 (2016)

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A solar flare is an intense burst of energy released at the surface of the Sun. It is caused by a process known as magnetic reconnection. The rotation of the Sun occurs at different rates depending on latitude. It has a rotational period of about 25 days at its equator, but about 34 days near the poles. This means the equatorial regions of the Sun rotate faster than the polar regions. Because of this differential rotation, the magnetic field of the Sun is twisted, so that over time the field lines of the magnetic field gradually wrap around the Sun.

You can visualize a magnetic field by thinking of field lines running from the North pole to the South pole. For the Earth’s magnetic field, the lines basically run from North to South, similar to longitude lines. The Sun’s magnetic field lines might start in a similar shape, but because the equator rotates faster than the poles, the lines twist around the Sun near the equator.

But the magnetic field lines would like to simply run North to South. So when they are twisted tighter and tighter around the equator region, they reach a point where they snap back into place, which is known as magnetic reconnection. When this happens a great deal of energy is released, causing a solar flare.

Solar flares are categorized by how intense they are at a specific x-ray frequency. The most intense category is known as an x-class solar flare. The smaller classes are further broken into a linear scale from 1 to 9. Since the x-class is an open class, its number ranking is a doubling scale, so that X3 is twice as powerful as X2. Some recent solar flares ranged from from X1.7 to X3.2.

While it is a bit unusual to see many x-class flares in rapid succession, flares of this size are completely normal during the Sun’s active period. While flares of this size can have an impact on satellites, the only impact for most people is a glimpse of northern lights if we happen to be at the right latitude.

Intense solar flares can have larger effects on us, such as causing power outages. In 1989 an X15 solar flare triggered a regional blackout in Quebec. So when solar flares hit the news there are the range of websites predicting the dreaded “big one”. Theses sites often reference the “Carrington Event” of 1859, which was so intense it produced northern lights as far south as the Caribbean. It also induced currents in telegraph lines. The storm induced enough current in the lines that messages could be sent across them even while the lines were disconnected from their power supplies.

If such an event occurred today, it would likely cause massive blackouts worldwide. It could cause trillions of dollars in damage, and would take several years to fully recover. It would be a massive disruption, but it wouldn’t be the end of civilization. Fortunately, studies of ice cores indicate that solar storms such as the Carrington Event only occur about once every 500 years, and there is no indication that such an event is likely to happen any time soon.

Still, if you want to keep tabs on the Sun’s flare activity, check out the space weather website.

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A while back I wrote about a new discovery of a dramatic rise in carbon 14 (C14) in the atmosphere around 774 AD.  Carbon 14 is radioactive, and decays over time.  It is one of the ways we can date the age of living things long after they’ve died.  The reason is because carbon 14 is generated in the atmosphere when high energy particles strike nitrogen atoms in the upper atmosphere, and living thing utilize that carbon while they are alive.  Once they die the carbon 14 in them isn’t replenished, so as the carbon 14 decays it over time it gives us a measure of how long an organism has been dead.

Since the level of carbon 14 in the air varies over time, we to account for that historical change when determining the age of objects.  Currently we have a calibration table which is accurate to 1% over about 29,000 years.  While this is an accurate table, we don’t often have measurements of the levels down to a specific year.  But in the article from January, a team was able to measure the C14 levels within the tree rings of two Japanese cedars.  Since we know the age of the rings, we can connect the specific C14 levels to a specific year.

What the team found was a 20% increase in C14 around AD 774-775.  Since C14 is generated by high-energy particles striking the atmosphere, this would imply either a solar flare or supernova occurred at that time.  In the January paper they argued that the rise was too big for a solar flare, and that it was likely due to a supernova.  One of the problems with the supernova idea is that it would have needed to be large, and there is no historical evidence of such a supernova at that time.  Although as +Alun Salt pointed out, given the difficulty with historical records, that isn’t too unexpected.

This month in Astronomy and Astrophysics a new article has been published on the subject.  A new team has looked at another set of tree rings.  This time from German oak trees.  What they found was the same C14 spike as measured in the Japanese cedar trees.  This confirms that the spike was a global event, just as we would expect from a supernova or solar flare.

But in calculating the C14 levels they found the first team had overestimated the rise.  This meant it was possible that the spike was caused by a solar flare, and not a supernova.  They then looked to historical records of that period looking for reports of aurora borealis (northern lights) at lower latitudes.  While northern lights are relatively common at higher latitudes, they are only seen at lower latitudes when there is particular strong solar activity.

The team found reports from China, England, Ireland and Germany from AD 772 – 778 that would seem to be observations of northern lights.  It would seem then that this spike was due to solar flares after all.

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