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Sydney scientists discover hundreds of star quakes: First results from NASA's Kepler Mission



5 January 2010

Astronomers at the University of Sydney are using data from NASA's Kepler Mission to learn more about the future fate of the Sun. After 300 days of intense investigation since the Kepler spacecraft launched in 2009, the scientific team behind Kepler is announcing the first results from the mission on 5 January 2010.

Star quakes: new data from the NASA Kepler mission shows what happens to stars as they age and the stellar light variability caused by star quakes. This diagram shows Kepler data of the stellar light variability caused by star quakes in four stars in the cluster NGC6819. The typical period of the stellar light variability reveals the increasing size of the stars as you move up the diagram, with larger stars having longer periods. As stars age, they move from the lower right to the upper left in the diagram (white arrows). Stars in a cluster are formed at the same time but with different masses. Although these stars share a common age, we see some stars (less massive stars) down at the bottom, while others (heavier stars) have already become red giants (top right) because heavier stars age faster.
Star quakes: new data from the NASA Kepler mission shows what happens to stars as they age and the stellar light variability caused by star quakes. This diagram shows Kepler data of the stellar light variability caused by star quakes in four stars in the cluster NGC6819. The typical period of the stellar light variability reveals the increasing size of the stars as you move up the diagram, with larger stars having longer periods. As stars age, they move from the lower right to the upper left in the diagram (white arrows). Stars in a cluster are formed at the same time but with different masses. Although these stars share a common age, we see some stars (less massive stars) down at the bottom, while others (heavier stars) have already become red giants (top right) because heavier stars age faster.

Dr Dennis Stello, an astrophysicist in the School of Physics at the University of Sydney, leads a team of 60 international scientists in the Kepler Asteroseismic Science Consortium, studying star quakes. Star quakes can be used by scientists to explore the interiors of stars, just as geologists use earthquakes to explore Earth's interior.

The group at the University of Sydney, who specialise in studying star quakes - an emerging field called asteroseismology - has found star quakes in over one hundred stars using the data from Kepler.

"The great power of Kepler, compared to previous space telescopes, is its extremely high precision measurements of star light over very long periods of time for an unprecedented large number of stars," explained Dr Stello.

"This makes Kepler the first instrument capable of finding habitable Earth-sized planets in orbits around distant Sun-like stars, and enables us to detect star quakes in the stars themselves," said Dr Stello.

"By studying star quakes we obtain a tool to 'look' inside the stars observed by Kepler."

In collaboration with an international team of more than 100 scientists, they have demonstrated that conducting asteroseismology on old puffed up stars known as red giants - the ultimate fate of our Sun - is even more exciting and promising than anticipated.

Professor Tim Bedding, also from the School of Physics at the University of Sydney and working on the Kepler data, is thrilled with the new results. He said, "With these new data on hundreds of stars from Kepler it looks like we will be able to figure out how our Sun will evolve when its hydrogen has been exhausted and it becomes a red giant."

Some of the stars investigated by the team belong to a star cluster - a group of stars born simultaneously about 2.5 billion years ago from a big cloud of gas and dust.

"In fact most stars, possibly including our Sun, were born in clusters. The detection of quakes in star clusters is therefore a tremendously exciting result that scientists have tried to achieve for decades," said Dr Stello.

Their results show that star quakes can be used to determine physical properties of stars, such as their size, and that this can be done for stars in quite different stages of evolution.

On left: An illustration of an oscillating star - stars oscillate and change their brightness periodically. On right: A comparison of the periods of oscillations for two stars - our Sun and Alpha Centauri A. The periods of oscillations are different for the two stars reflecting the different size, age and structure of those stars. A star will oscillate in several periods simultaneously and through mathematical analysis, the Kepler scientists will construct a diagram where all the individual periods can be measured from the measurements of brightness variations over the length of the Kepler Mission.
On left: An illustration of an oscillating star - stars oscillate and change their brightness periodically. On right: A comparison of the periods of oscillations for two stars - our Sun and Alpha Centauri A. The periods of oscillations are different for the two stars reflecting the different size, age and structure of those stars. A star will oscillate in several periods simultaneously and through mathematical analysis, the Kepler scientists will construct a diagram where all the individual periods can be measured from the measurements of brightness variations over the length of the Kepler Mission.

"This first step will probably lead to completely new explorations of the formation and evolution of stars," said Dr Stello.

Also announced by NASA on 5 January 2010, are a number of new planets detected by Kepler. The planets are not detected by direct imaging, but the Kepler team uses the spacecraft to reveal their existence by measuring the planet transits - which are tiny dips in the star light as the planet moves across the stellar disk - partially eclipsing the star for several hours.

To fully understand the new planetary systems detected by Kepler, NASA has recruited to the Kepler team a number of asteroseismologists, including the team at the University of Sydney.

The Kepler Telescope was launched in March 2009 in an orbit around the Sun to measure the light from more than 100 000 stars continuously over the four year mission. The huge amount of data from all the stars observed by Kepler is yet to be analysed in full.

"These first results are only the beginning, and in the coming years even more fascinating results are expected to emerge. Based on the quality of the data we have seen so far we have extremely high expectations for this new decade," said Dr Stello.

"Anticipate nothing less than a revolution in our understanding of stellar structure and evolution."

The scientific papers reporting these discoveries will be published in a special issue of the Astrophysical Journal and are available at: http://xxx.lanl.gov/

Read Dr Stello's and Professor Bedding's group papers on star quakes in the Astrophysical Journal at: http://xxx.lanl.gov/abs/1001.0026 and http://xxx.lanl.gov/abs/1001.0229


Contact: Katynna Gill

Phone: 02 9351 6997

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