23 April 2008

Solar flares leave Sun quaking

Cosmos Online
Violent explosions in the Sun's atmosphere have been linked to 'starquakes' on its surface, a discovery that may one day help protect astronauts from dangerous radiation.
Solar flares leave Sun quaking

Quake formers: Solar flares in action on the surface of the Sun. This artificially coloured image of the Sun's corona was captured by SOHO near the peak of the eleven-year cycle of solar activity in 1999. Credit: SOHO/NASA

SYDNEY: Violent explosions in the Sun’s atmosphere have been linked to ‘starquakes’ on its surface, a discovery that may one day help protect astronauts from dangerous radiation.

These explosions – called solar flares – are caused by a release of magnetic energy in the ionised gas of the Sun’s atmosphere. A single solar flare gives off the same amount of energy as millions of 100-megaton hydrogen bombs exploding simultaneously.

Experts already knew that the energy from solar flares causes small tremors in the surface of the Sun. Now a new study reveals that the flares also cause a larger phenomenon; something akin to the earthquakes we experience here on Earth, but with significantly more energy.

Monster quakes

The possibility of a connection between solar flares and starquakes, was first mooted in 1972, but remained unproven until now.

“In some sense, the scientific community have been waiting 36 years for this result so its significance is huge,” said astronomer Christoffer Karoff at the University of Aarhus in Denmark. Karoff and co-researcher Hans Kjeldsen publish their results in The Astrophysical Journal this month.

A typical ‘sunquake’ or ‘starquake’ rates 11.3 on the Richter scale, say experts, an energy level never before reached by an earthquake. This is the equivalent of 40,000 times the energy released by San Francisco’s infamous 1906 earthquake.

Previously, it was believed that turbulent motions in the outer layers of the Sun caused the smaller tremors. According to Karoff, this is analogous to a bell sitting in a desert sandstorm: as each grain of sand hits the bell, it rings weakly.

However, the data collected by Karoff shows that the metaphoric bell sometimes rings with much more purpose. “What we have seen is [something] that every once in a while comes up and knocks the bell with a hammer so it rings [loudly] for a short while. The flares are the hammer.”

In order to see the correlation between the solar flares and the sunquakes – or to ‘hear’ the bell ringing – Karoff and Kjeldsen sifted through 10 years of solar observations from the Solar and Heliospheric Observatory (SOHO), jointly operated by the European Space Agency (ESA) and NASA.

Space weather forecasts

The discovery of the link increases our understanding of the Sun’s internal processes and could help researchers to predict solar flares. This is important because solar flares eject plumes of plasma into space, and the associated radiation can be dangerous to astronauts, and interfere with power plants and electronic equipment here on Earth.

“This new result is very interesting and quite surprising,” said Bernhard Fleck, a SOHO team scientist at the U.S. space agency’s Goddard Space Flight Centre in Maryland. “We thought that we had understood the excitation of the global solar oscillations.”

SOHO uses 12 complementary telescopes and other instruments to collect data on solar oscillations, the Sun’s energy output, plasma flows, flares, eruptions, and solar wind, added Fleck.

According to Karoff, the next step for the researchers is to analyse a few single flares in more detail to put together a model of exactly how the energy from the solar flares is transformed into the sunquakes.


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