‘Breakthrough’ erupts from study of the sun
Proof is found for long-theorized nanoflares, which may fuel the corona’s heat.
One of the greatest mysteries of how stars behave has been right in our own backyard: the sun’s corona. Scientists have long wondered what heats this thin, ethereal shell of particles to hundreds of times the temperature of the surface of the sun.
Now, after combining evidence from a sounding rocket and a black-hole-hunting telescope and employing computer modeling, researchers say they’ve found the cause: nanoflares.
“We have for the first time direct proof that nanoflares exist and heat the corona,” said Jim Klimchuk, a solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “This proof takes the form of superhot plasma.… It’s a real breakthrough.”
The findings, described at the first Triennial EarthSun Summit meeting underway in Indianapolis, may help solve the decadesold mystery of what powers the corona and help scientists better predict the effects of space weather on Earth.
While the sun’s surface is about 10,000 degrees Fahrenheit, the corona, which extends high above the surface and into space, burns at temperatures of about 4 million degrees, and can even hit 18 million degrees in some spots.
Scientists have been stumped in explaining how this wispy shell of ionized gas can get superheated to such extremes.
Researchers have long suspected that nanoflares exist and might account for the corona’s mysterious heating source.
Nanoflares, so called because they’re one-billionth the size of typical solar flares, are still powerful, packing the equivalent energy of a 10-megaton hydrogen bomb.
Though they’re small by the sun’s standards, there are many of them — millions going off each second on the sun’s surface.
Researchers working on different lines of inquiry each say they’ve found strong evidence that nanoflares exist.
Scientists flew a sounding rocket equipped with an instrument called the Extreme Ultraviolet Normal Incidence Spectrograph for 15 minutes, looking for signs of superheated gas (the areas that can hit 18 million degrees Fahrenheit).
Using this instrument, known as EUNIS, lead scientist Adrian Daw, a solar scientist at Goddard, was able to find those bits of gas.
“That superhot plasma emission that we’re seeing there is the smoking gun of nanoflares,” Daw said.
Scientists also used NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, to look for evidence of nanoflares. NuSTAR is used to study the X-rays coming from black holes, among other high-energy phenomena, but it can also be used to study X-ray emissions coming from regions of the sun where normal-sized flares could not be detected.
These regions were popping with X-ray energy, a sign that nanoflares were at work, Iain Hannah, an astrophysicist at the University of Glasgow in Scotland, said in a media briefing in Indianapolis.
The scientists think these nanoflares are caused by the twisting and breaking of magnetic field lines around the sun, Klimchuk said, though it will be a while before they can study exactly how the nanoflares work.