Good Vibrations

Ever wonder what a star sounds like?
Stars certainly aren’t silent. Actually, they constantly ‘sing’ by oscillating at certain frequencies. Using ESA’s Corot satellite, astronomers have recorded these frequencies and made them into actual sounds. Click that link above to go to the BBC website and actually hear starsong!
(Much scintillation and sparklyness to Arianna for e-mailing that link!)

Obviously, actual sound doesn’t travel through space. What you’re hearing are the frequencies the star’s vibrating at after they’ve been recorded by astronomers here on Earth. The tone is affected by a star’s age and how many metals it contains. The fluctuations you hear come from the fact that the whole star is oscillating. Vibrating standing waves ripple through the star’s body, and they can tell you a lot about the internal workings of the star itself.

In fact, they’d look something like this (for geeks and scientists, that’s a l=5, m=4 p-mode vibration). This is just one of well over a million different ways a star can vibrate. It’s overemphasised, of course, but the Sun is vibrating this way even as you read this.

The technique’s called astroseismology. It all started around 1962, when a group studying the Sun noticed that the radiation emitted by the solar surface slowly changes with a period of about 5 minutes. Specifically, they were looking at lines in the Sun’s spectrum, and noticing tiny doppler shifts over time. What they’d found were the acoustic harmonics in the Sun’s surface.

Actually, this site has recordings of some more starsong.
As you’d expect, giant stars have a deep throbbing sound, while tiny, rapidly spinning white dwarfs are full of odd harmonics. You can even compare Alpha Centaurii A with Alpha Centauri B.

In a manner somewhat reminiscent of the molecular vibrations I study, stars have a number of different vibrational modes. The big difference is that while miniscule molecules have a handful of possible vibrations stars are enormous, so they have millions! The whole concept (with some more pretty visualisations of vibrating stars) is explained really rather well on this webpage, courtesy of St Mary’s University’s David Guenther.

The technique of actually listening to these vibrations, however, is a relatively new one; though it’s fast becoming popular. More and more astronomers (such as Jodrell Bank’s Tim O’Brien) are listening to sounds from space. It’s easy to see why, with the eerie beauty of some of these sounds, though it’s also a very useful scientific method!

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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