Our Sun, solar flares and the neighbour’s superflares

Our Sun is a pretty quiet star, it’s not known for planet destroying outbursts and it generally maintains a fairly constant output. We’ve got better at observing it and have noticed 11 year cycles of activity, of which we’re currently in a minimum period. The Sun is about half way through it’s hydrogen in the core so should be good for another 5 billion years or so. I’ve always been fascinated at how lucky we are to have such a stable star, because could have been quiet different, or not at all. Recently there were observations of a significant superflare (not a pair of 1970s trousers) by our nearest stellar neighbour, other than the Sun, which would have easily sterilised any orbiting planet. It just showed how precarious life might be out in the universe.

Large solar events have become more noticeable to humans since we started mucking around with technology. The Carrington event of 1 September 1859 induced one of the largest geomagnetic storms on record. It was caused by a huge coronal mass ejection (CME), which sent a massive inundation of charged particles to the Earth’s magnetosphere. This was a very active period for the Sun with aurora being visible much closer to the equator than normal in places like the Caribbean, Columbia and Queensland in Australia. Telegraph systems around the world failed and many other weird occurrences were observed. The picture below is of the observations made by Richard Carrington of the sunspots on the Sun on 1 September 1859.

There have been other storms including one in 1989 that knocked out power in Quebec, Canada. In 2012 another event of similar size to Carrington occurred but missed Earth’s orbit. The cost and damage likely to occur if another 1859 type event occurred would be staggering and in the order of trillions of dollars. These events are tiny compared to what other stars are capable of. The mechanism that causes these massive solar outbursts is basically due to the magnetic field lines getting so twisted and deformed that they suddenly snap releasing an enormous amount of energy. The currents on material within the Sun and difference in rotation speeds at different layers all conspire to twist and tangle magnetic field lines.

Some stars release solar flares over 10,000 times bigger than the biggest flare from our Sun. These are called superflares and have been the subject of study for sometime. Scientists have found a correlation between rotation speed and the number of superflares but also many of them on stars like our own Sun so the mechanism behind them is still not very well understood. Research done with Kepler 2 data showed quite a variation in the frequency of these superflares on G-type dwarf stars (our Sun is one of these). Some stars showed frequencies of 500-8000 years and others with as much as 1 every ten days. The researchers found a correlation between sunspot size and flare intensity. The damage done by a superflare on Earth would be catastrophic.

A sunspot on the Sun (Credit: the author)

When a planet was discovered in the habitable zone around Proxima Centauri there was much hope that this be a spot where life could have developed, and being so close to our Solar System it might even be possible to detect. This hope was quickly dashed when it was found that this star pumps out about 5 superflares per year. Being so close, scientists were able to observe Proxima Centauri’s flares in some detail and determined the size of the flares at about 10^35 ergs (Carrington was probably about a 10^33). At that level the ozone layer of the atmosphere is severely damaged which allows in damaging UV light. In the case of Proxima Centauri, it is producing these flares multiple times a year, bathing the planet with more and more UV light and stripping any protective ozone, that might have been there.

So maybe life there is not as we know it!

Back on Earth, we are lucky to have a quiet Sun that’s still very quiet even when we think it’s being violent.