Measuring the age of stars much older than the sun
12 March 2009
A team of scientists from the School of Physics are leading research to measure the ages of stars that are much older than our sun, using data from NASA's Kepler spacecraft.
Kepler, launched on 6 March 2009 from the Cape Canaveral Air Force Station in Florida, USA, will collect detailed data on a section of space for at least three and a half years, looking for rocky planets similar in size to Earth.
Using Kepler, NASA expects to answer a very fundamental question: do planets the size of Earth exist in orbit around other stars? The Kepler mission will not only search for planets around other stars, but also yield new insights into the parent stars themselves.
"Kepler has a large telescope that will measure the variations in brightness of 170 000 stars simultaneously and continuously over the three and a half year period," said Dr Dennis Stello, from the School of Physics, who leads two international Kepler research groups.
"The two teams I lead are working on understanding stars much older than our sun and stars located in stellar clusters. Each group has around twenty to thirty members from around the world in it.
"We are tremendously excited to be part of this international project, which will give us the opportunity to study a large variety of stars and extend our seismic techniques to measure the ages of these older stars."
Dr Laszlo Kiss, a Senior Research Fellow in the School of Physics, is leading another Kepler team looking at Mira stars, while other School of Physics scientists are involved in other Kepler research teams.
Kepler's measurements of changes in stellar brightness will be used to study stars and their interiors. The small variations in a star's light will be picked up by Kepler's precise photometry, which can then be used to measure if the surface of a star is oscillating.
"Stars, like our sun, can ring like a bell due to sound waves which result in oscillations of the whole star. We'll measure these oscillations by conducting 'stellar seismology' - in a similar way to how geologists probe the Earth's interior using earthquakes which make waves move in the Earth's interior," explained Dr Stello.
"If the surface of the star is oscillating, Kepler will detect periodic variations in the brightness of the star, and by measuring the brightness fluctuations over time spans from weeks to months to years, we'll be able to measure the precise periods of those stellar oscillations."
Dr Stello and his team will use these seismic techniques to probe the cores of a large number of stars, allowing them to determine the size, chemical composition and rotation rate of stars.
"For those stars that have planets orbiting, we'll be using stellar seismology to determine the star's age. We're interested in discovering whether stars that host planets have the same age as our sun and if the planets are as old as our Earth."
The quality of the Kepler data and the large number of stars observed are expected to lead to a huge step forward in understanding of stellar evolution. During the first nine months in space, Kepler will survey more than 5 000 stars for oscillations. Based on those measurements, around 1 100 stars will be followed for detailed studies throughout the full mission.
"Kepler's measurements of stellar oscillations is so highly accurate that we expect for the first time ever to directly watch the change in stars as they age," said Dr Stello.
"This huge quantity of new data will lead to a much improved understanding of the evolution of stars and hence, ultimately, of the universe in which they reside."
The University of Sydney team are some of the 200 researchers from 50 institutions from around the world who make up the Kepler Asteroseismic Science Consortium, who are analysing the enormous data set collected by the Kepler spacecraft. Other groups are focusing on data which will answer other questions about stars in our galaxy such as whether our sun is a typical star, how stars evolve, and how matter behaves under the extreme conditions in stars.
The spacecraft Kepler is named after Johannes Kepler (1571-1630), a historically important astronomer who provided systematic evidence to support the Copernican theory that the Earth revolves around the sun and was the first to develop laws of planetary motion.
Learn more about NASA's Kepler spacecraft at: http://kepler.nasa.gov
Contact: Katynna Gill
Phone: 02 9351 6997