Image: ALEXANDRA CHAMBERS and DARRAN BAKER |
An international team of astronomers has measured the exact "heartbeat" of a pulsating star 24 light-years away¿confirming theoretical predictions and getting a glimpse of what may become of our own sun a few billion years from now. The star they studied¿beta Hydri in the southern constellation Hydrus¿is about 2.5 billion years older than our sun. But like the sun, gases in beta Hydri's outer layers produce sound waves that make its surface quiver and shake (see animation at right).
Whereas these oscillations on the sun have a period of about five minutes, the scientists expected beta Hydri's pulse to be much slower¿having a period closer to 15 to 20 minutes. "As a star gets older, its 'voice' deepens," says team leader Tim Bedding of the University of Sydney in Australia. In fact, that is just what they found.
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To measure the distant oscillations¿which move only half a meter per second¿the researchers tracked small changes, or Doppler shifts, in the spectrum of the light coming from beta Hydri¿a technique usually employed to hunt down extrasolar planets. Using the 3.9-meter Anglo-Australian Telescope near Coonabarabran, Australia, they sampled the star light every two minutes for five nights in a row¿making 1,200 observations in all. In the end, they discovered that the surface pulsed in and out every 17 minutes.
"We will use the technique to check basic facts about stars," Bedding notes. "So much of what we think we know about the universe rests on the ages and properties of stars. We could find that our current ideas are wrong." For instance, he points out that "the theories of convection are pretty crude at present. We hope this technique for measuring oscillations can be used to test them. That sort of finding could change how old we think stars are."
Next up, they plan to analyze alpha Centauri A near the Southern Cross constellation. And they look forward to the 2004 launch of an Australian-built telescope called MONS (Measuring Oscillations in Nearby Stars).
