Currently, the Sun is supposed to be entering the quietest phase of its 11-year cycle, but that hasn't stopped it from blasting forth some of the largest solar flares on record. Sunspot region 2673 has now turned away from Earth, but not before unleashing several X-class flares over the past week, one of which is the largest in over a decade and one of the top 10 since records began.
Created by the Sun's twisting magnetic field, solar flares are bursts of light and energy from the surface of our star, and their energy is measured according to a scale of A, B, C, M and X classes, where each letter is 10 times the strength of the previous one. Often accompanied by bursts of energetic particles called Coronal Mass Ejections, M- and X-class eruptions can interfere with radio, GPS, and even ground-based communications and power grids.
After a few M-class solar flares early last week, the show really kicked off on September 6, when that sunspot gave rise to three X-class flares over two days. Bookended by much smaller X2.2 and X1.39 flares, the largest was a huge X9.3 eruption, followed by another X8.2 on September 10.
"The Sun is currently in what we call solar minimum," says Aaron Reid, from Queen's University Belfast's Astrophysics Research Centre. "The number of Active Regions, where flares occur, is low, so to have X-class flares so close together is very usual. These observations can tell us how and why these flares formed so we can better predict them in the future."
Since flares spring forth in a matter of minutes, it can be difficult to observe the beginning of their formation. Astronomers using the Swedish Solar Telescope managed to do just that, not once, but three times in a row. These observations can help astronomers better predict solar storms in advance, to help astronauts and organizations prepare for any disruptions.
"It's very unusual to observe the opening minutes of a flare's life," says Chris Nelson, of Sheffield University's Solar Physics and Space Plasma Research Centre. "We can only observe about 1/250th of the solar surface at any one time using the Swedish Solar Telescope, so to be in the right place at the right time requires a lot of luck. To observe the rise phases of three X-classes over two days is just unheard of."
These are the first X-class flares since May 2015, and the X9.3 ejection was the eighth strongest since records began in 1996. It was the most powerful since an enormous X17 flare burst forth in 2005, but even that doesn't stack up against the most intense solar flare ever seen. That honor goes to a flare from 2003 that overloaded the sensors trying to measure it, which topped out at a staggering X28.
Check out the X9.3 flare in the video below.