Ultra-impulsive acoustic emission from a solar flare recently detected by NASA’s Solar Dynamics Observatory (SDO) indicated submersion of its source beneath the active region that hosted the flare.
Flaring, active regions of the Sun are highlighted in this image combining observations from several telescopes. High-energy X-rays from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) are shown in blue; low-energy X-rays from Japan’s Hinode spacecraft are green; and extreme ultraviolet light from NASA’s Solar Dynamics Observatory (SDO) is yellow and red. All three telescopes captured their solar images around the same time on April 29, 2015. Image credit: NASA / JPL-Caltech / GSFC / JAXA.
Sunquakes release acoustic energy in the form of waves that ripple along the Sun’s surface, like waves on a lake, in the minutes following a solar flare.
Solar astronomers have long suspected that sunquakes are driven by magnetic forces or heating of the outer atmosphere, where the flare occurs.
These waves were thought to dive down through the Sun’s surface and deep into its interior.
On July 30, 2011, SDO observed a sunquake with unusually sharp ripples emanating from the M9.3-class solar flare.
Dr. Charles Lindsey from North-West Research Associates and colleagues were able to track the waves that caused these ripples back to their source, using a technique called helioseismic holography.
This technique, which used SDO’s Helioseismic and Magnetic Imager to measure how the solar surface was moving, has previously been used to track acoustic waves from a variety of other sources in the Sun.
Instead of the waves traveling into the Sun from above, the scientists saw the surface ripples of a sunquake emerging from deep beneath the solar surface right after a flare occurred.
The results found the acoustic source was around 1,127 km (700 miles) below the surface of the Sun — not above the surface as previously was thought.
Left frame shows the active region of the Sun in visible light (amber) and extreme ultraviolet (red) on July 30, 2011. Right frame shows the ripples on Sun’s outlying surface up to 42 min after the onset of the flare, which is marked by the label ‘IP’ for impulsive flare. Image credit: NASA / SDO.
“These waves were driven by a submerged source, which was in turn somehow triggered by the solar flare in the atmosphere above,” the astronomers said.
“The findings might help explain a long-standing mystery about sunquakes: why some of their characteristics look remarkably different from the flares that trigger them.”
“We still haven’t identified exactly what mechanism actually causes sunquakes, though the results do provide the clue that their origins likely lurk beneath the surface.”
“We plan to continue searching for a mechanism by looking at other sunquakes to see if they have similarly submerged sources.”
The findings were published in the journal Astrophysical Journal Letters.
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Charles Lindsey et al. 2020. Submerged Sources of Transient Acoustic Emission from Solar Flares. ApJL 901, L9; doi: 10.3847/2041-8213/abad2a
This article is based on text provided by the National Aeronautics and Space Administration.
