February 21, 2011

Kepler Helps Listen To The Music Of The Stars

Bill Chaplin from the University of Birmingham, speaking at the American Association for the Advancement of Science (AAAS) conference in Washington, said that the Kepler space telescope was an exquisite tool for what is called "astroseismology", measuring the sizes and ages of stars.

The Kepler telescope measures five times better than any other means as it "listens" to the sounds they make. The technique, used to measure some 500 far-flung stars, measures minuscule variations in a star's brightness that occur as soundwaves bounce within it.

Chaplin tells BBC News that astroseismology was, in essence, listening to the "music of the stars". Kepler's primary job however is spotting exoplanets, planets orbiting stars other than our own, by measuring the tiny dip in the amount of light that it sees when a planet passes in front of a distant star.

These precise light-level measurements also work for astroseismology, because as sound waves resonate within a star, they slightly change both the brightness and the color of light that is emitted. Researchers can measure the acoustic oscillations that gave rise to the ripples on the light that Kepler records.

The sounds are thousands of times lower than humans can hear and like a large musical instrument has lower the pitches, the bigger the star, the lower the pitch. There are overtones however - multiples of those low frequencies - just like instruments, and these give an indication of the depth at which the sound waves originate, and the amount of hydrogen or helium they are passing through.

Stars fuse more and more hydrogen into helium as they grow older giving astroseismologists a way to increase five-fold the precision of their age estimates for stars. "With conventional astronomy, when we look at stars we're seeing the radiation emitted at their surfaces; we can't actually see what's happening inside," Chaplin tells BBC News.

"Using the resonances, we can literally build up a picture of what the inside of a star looks like - there's no other way of doing that. It's not easy to do, but we're now getting there, thanks to Kepler."

Canada's Most and ESA's Corot satellites are designed specifically to collect data similar to the Kepler telescope, but just the first few months of observations by Kepler has provided scientists with data on hundreds of stars, whereas Dr. Chaplin said that only about 20 have been studied in detail Canada's efforts.

"Suddenly we have this huge database to mine," Chaplin concluded. "I could literally spend the rest of my research career working on these data - we're just starting to mine them."


Image Caption: Artist's rendition of Kepler spacecraft. Credit: NASA/Kepler mission/Wendy Stenzel


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