Pipe down, Sun

by Ian Johnson, CBC news online

OK, here's a quick word-association check: What comes to mind when someone says "sun"? Words like hot, bright and blazing, right? Well, how about noisy?

Scientists have known for years that the Sun produced sounds internally, but it was thought that the waves (which have very low wavelengths measured in hundreds of kilometres) were trapped below its surface. This week, the Goddard Space Flight Center reported that using spacecraft, ground-based telescopes and computer simulations, researchers have determined that Sun's magnetic field allows wave energy to be released from the interior. The field permits sound waves to travel through thin fountains of hot gas upward into a region of the Sun's atmosphere called the chromosphere.

According to NASA:

"The surface of the Sun produces sound waves because the surface is convecting and this produces pressure waves that travel into the inner corona. These pressure waves steepen into shock waves and this is possibly why the corona gets so hot ... In 'helioseismology' you can 'hear' the Sun ring like a bell. This is coherent sound produced by the vibration of the entire surface of the Sun caused by sub-surface convection. By studying all the different tones that the Sun vibrates in, astronomers can probe the deep interior of the Sun and discover just how deep the convection layers are, and also how fast the deep interior is rotating compared to the surface."

"The Sun's interior vibrates with the peal of millions of bells, but the bells are all on the inside of the building," Scott McIntosh, a researcher at Southwest Research Institute, Boulder, Colo., said in a report on Eurekalert regarding the latest research. "We have been able to show how the sound can escape the building and travel a long way using the magnetic field as a guide."

Not that anyone's going to be swinging by to listen any time soon, of course - which begs the question that if a
flare shoots from the sun and there's nobody around to hear, does it REALLY make a sound? The research was presented at the meeting of the American Astronomical Society's meeting in Honolulu, Hawaii.

In related news, the European Space Agency says its Solar and Heliospheric Observatory has discovered radio "screams" that warn of dangerous coronal mass ejections (CMEs), which produce radiation storms that can harm astronauts, as well as electronic gear both on earth and in space.

Huge CMEs accelerate electrons in the solar wind, producing the radio signal.

"Since the radio signal moves at the speed of light while the particles lag behind, we can use a CME's radio noise to give warning that it is generating a radiation storm that will hit us soon," said Goddard Space Flight Center's Natchimuthuk Gopalswamy in a statement. "This will give astronauts and satellite operators anywhere between a few tens of minutes to a couple of hours to prepare, depending on how fast the particles are moving."