The powerful belch of material ejected during a solar flare may be way hotter than scientists thought it was.
A new mathematical analysis suggests that the engine driving solar flares is far more effective at heating charged particles, or ions, than it is at heating electrons.
This could mean that we've been underestimating the Sun, since flare temperatures are estimated based on electron heating. The latest calculations show that ions in solar flares might reach a scorching 60 million Kelvin (60 million ºC, or 1.08 billion ºF).
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"Solar physics has historically assumed that ions and electrons must have the same temperature," explains astrophysicist Alexander Russell of the University of St Andrews in the UK.
"However, redoing calculations with modern data, we found that ion and electron temperature differences can last for as long as tens of minutes in important parts of solar flares, opening the way to consider super-hot ions for the first time."
Solar flares are powerful manifestations of the Sun's idiosyncrasies. Because the solar equator rotates faster than the poles, the solar magnetic field lines can get all tangled and twisted, causing them to snap and reconnect, releasing a vast amount of energy. This energy has to go somewhere; et voila, solar flares.
That released energy heats the ejected material and the solar atmosphere to more than 10 million degrees Celsius – far, far hotter than the Sun's baseline surface temperature of around 5,500 ºC, or even the Sun's coronal temperature of 2 million ºC. (Yes, the Sun's atmosphere is hotter than its surface – you can read about that mystery here.)
Solar flares also release powerful bursts of X-rays and gamma radiation; although these energetic forms of light can't penetrate Earth's atmosphere to the surface, they can disrupt communications that rely on the upper atmosphere, interfere with satellite and spacecraft operations, and pose a hazard to human astronauts in low-Earth orbit.
For these reasons, scientists want to be able to understand solar flares in detail.
Solar flare plasma is made up of electrons and ions. Previously, it had been assumed that both were heated the same way in solar flares. However, looking at other recent works, Russell and his colleagues realized that this assumption may be incorrect.
"We were excited by recent discoveries that a process called magnetic reconnection heats ions 6.5 times as much as electrons," he says. "This appears to be a universal law, and it has been confirmed in near-Earth space, the solar wind, and computer simulations. However, nobody had previously connected work in those fields to solar flares."
Applying the conclusions of other works to solar flares, the researchers found that ions in these outbursts could get as hot as 60 million ºC – a finding that may explain some heretofore unresolved features of solar flare spectra that scientists have puzzled over for decades.
At the moment, this is purely theoretical, of course. More work needs to be done to validate the finding. However, now that scientists know about this possibility, they can design experiments and observation regimes to test for it.
The analysis has been published in The Astrophysical Journal Letters.