In July 2011, astronomers spotted several circles on the surface of the sun that appeared to be laced together in a distinct pattern like a pond wave.
Scientists call this event a “helioseism,” as earthquakes occur on Earth, a tremor in the Sun for some reason. Previously, scientists speculated that it was caused by an intense flare eruption on the sun’s surface.
A recent study published in The Astrophysical Journal Letters traced the source of the unexplained event that caused the sighting – not from the surface of the sun, but from a depth of seven hundred miles below the surface.
Astronomers first discovered the helioseism from data collected by NASA’s Solar Observatory in 1998. A helioseismic signal of magnitude 11 was monitored immediately after a solar flare eruption.
Earlier, in 1972, an astronomical research group proposed a theory that such an event would occur on the Sun. They believed that an intense solar flare would cause the temperature inside the Sun to rise, resulting in a mechanical pulse and a helioseism.
Despite this theory, not every flare event triggers a helioseism, and the phenomenon has only been seen in a few specific regions of the Sun’s surface so far, so what exactly is going on with helioseisms remains a mystery.
Understanding the size and evolution of helioseismic events is important for understanding the nature of solar flares and the physical mechanisms within the Sun. In fact, prior to this study, scientists were unable to pinpoint the source of these ripple events.
Some believed that helioseismic events were a result of magnetic fields or the heating of the Sun’s outer atmosphere by flares, while others believed that the effects of these ripples would reach below the Sun’s surface and that their influence could reach deep into the Sun’s interior.
But this new study proves a completely different story. Scientists used a technique called helioseismic holography to analyze data from the ripples captured after the intense flare in 2011. The nature of these ripples is sound energy, but the helioseismic holography technique was able to measure how this energy moved across the surface of the sun.
To the researchers’ surprise, the ripples came from deeper below the Sun’s surface – about seven hundred miles deep. Scientists still do not know the underlying cause of these sound waves, only the exact location of their source.
The next step for this research group will be to observe more helioseismic data to see if the source of the flares and the subsurface tremors are the same.
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