Focused Solar Explosions Get Hotter
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An image of the solar flare taken using the X-Ray Telescope onboard Hinode on June 7, 2007. This shows the flare loops in the solar atmopshere at temperatures exceeding 10 million degree Celsius. (Credit: Courtesy of JAXA)
ScienceDaily (Apr. 7, 2008) — Using data from the Hinode and RHESSI solar observatories, astronomers have discovered that solar flares - explosions in the atmosphere of the sun - get much hotter when they stay "focused".
Dr Ryan Milligan of Oak Ridge Association of Universities, Tennessee, who is stationed at NASA’s Goddard Space Flight Center in the US, will present his result on Wednesday 2 April at RAS National Astronomy Meeting in Belfast.
Solar flares are caused by the sudden release of magnetic energy. The largest can release as much energy as a billion one-megaton nuclear bombs. However, the flare observed in this study was a much more common "micro" flare. Researchers at space agencies like NASA and ESA want to understand flares because they generate radiation that can be hazardous to unprotected astronauts, like those walking on the surface of the Moon.
"A flare typically divides its energy between directly heating the solar atmosphere and accelerating particles," said Dr. Milligan. "These unusual flares seem to focus on one task, devoting all their energy to heating. This allows them to become millions of degrees hotter than their multi-tasking cousins."
Flares normally occur above loops of electrically conducting gas, called plasma, in the Sun's atmosphere. When a typical flare goes off, it heats the plasma and sends beams of electrons racing down the sides of the loops. The electron beams evaporate more plasma from the Sun's visible surface, which expands back up the loops.
"This evaporated plasma has traditionally been believed to be the source of the hottest temperatures seen in solar flares," said Dr Milligan. "However, the flare in this new observation reached a temperature of 15 million degrees Celsius - some five million degrees hotter than expected for a flare of this size - without any evidence for beams of accelerated electrons."