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Stellar Senior Citizens Shed Light on Sun"s Demise
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
05 February 2001
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Animation captions On Earth, the older generation constantly exasperates younger folks by having all the answers and telling how it used to be. Now some astronomers have turned that analogy to their advantage by looking at an older star to see what it reveals about the future of our own, young and relatively inexperienced Sun.Beta Hydri is about the same size and temperature as our Sun but it is nearly twice as old -- about 7 billion years old -- and it is taking the last puffs of the hydrogen fuel that powers its thermonuclear core. Nonetheless, this senior citizen of stars still has a "pulse" -- it's slow but it's there. To get that measurement, the astronomers studied periodic variations in the speed of gas moving on or near the surface of the star. The measurements provide clues to the star's internal structure that will help test models and theories of stellar evolution. The work might also help scientists figure out how our Sun will die. | The Sun"s Pulse | | Using sound waves to peer a third of the way into the Sun, researchers found vast pools of hot, electrified gas rubbing shoulders as they moved at different speeds. The activity may fuel sunspots. Learn more. | "Beta Hydri gives us a good idea of what the Sun will look like in a few billion years," says Tim Bedding of the University of Sydney. Inside the Sun Scientists discovered in 1979 that the Sun oscillates every four to eight minutes in various modes. Each mode represents a different pattern of sound waves, and the period of each one gives information about the speed of the sound in the part of the star where the sound wave spends most of its time. As an example, the speed of sound in helium is less than it is in hydrogen. Since the thermonuclear reactions inside a star convert hydrogen to helium, measuring sound waves helps researchers figure out if the hydrogen tank is mostly full or mostly empty.The technique, which is much like the one used by seismologists to probe Earth's interior, provides insight into a star's overall temperature, rotation, composition and age. Since Beta Hydri is older than the Sun, the oscillation periods were expected to be longer, on the order of 15 to 20 minutes. Indeed, the researchers measured the period at 17 minutes. "Detecting these seismic waves on Beta Hydri is like feeling the pulse of the star," said Paul Butler of the Carnegie Institution of Washington. "Just as a person's pulse reveals information about the heart, these oscillations allow us to peer deep into the center of the star to tell us about conditions there." The researchers studied Beta Hydri, which is 24 light-years away, with the 154-inch (3.9-meter) Anglo-Australian telescope. Results of the research, which was supported by the National Science Foundation, will be published in an upcoming issue of Astrophysical Journal Letters. Click here for more news and information about the Sun, as well as stars and other deep space objects.
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