Astronomers have found a tool to probe deep into the heart of a dying star, known as a red giant.
The discovery reported in the journal Science, will help researchers understand the eventual fate the Sun, when it dies in about 5 billion years time.
One of the paper's authors, astroseismologist Professor Tim Bedding from the University of Sydney, says his team used NASA's Kepler space telescope to look for oscillations in a distant swollen red giant called KIC 6928997.
Bedding says just like seismologists using earthquake vibrations to probe the Earth's internal structure, astronomers can use oscillations or pulsations in the brightness of stars to learn about their structure.
"By looking at the fluctuations of the light, we can measure the periods of the oscillations which are a repetitive motion of expansion and contraction of the star due to waves bouncing around inside," he says.
Searching for patterns
Bedding and colleagues used a mathematical technique called Fourier analysis to look for distinctive patterns, eventually finding 20 different oscillation signals.
"We needed 320 days of Kepler observations to disentangle the complicated oscillations of the star," he says. "It's oscillating in many different patterns simultaneously. It's very subtle, but indicates waves from the very centre of the star are making their way to the surface."
According to Bedding, stars aren't uniform, but get hotter and denser towards the core. Patterns in these oscillations indicate changes in density.
"We'll be able to learn about their density and temperature. As you go inside them, does it go up gradually or all of a sudden?" he asks.
"And the bit in the middle is where the action happens, where nuclear fusion takes place. There are no nuclear reactions happening at the surface."
"Red giants are much bigger than the Sun, but the region where the nuclear reactions happen is relatively small. Probing that region and finding out what's happening there, whether there's [just] hydrogen, or whether there might be helium fusing as well, those are the things we're going to be looking at."
More than just theories
According to Bedding the research is proof of concept.
"Before these observations there were only theoretical papers predicting what you could expect to see inside a red giant," he says.
"This particular subtle pattern (we call them gravity modes), of oscillation deep inside the star, were predicted to be there. So the fact that we saw them was a wonderful confirmation."
"The next step is to use them to do science to learn more about these stars, and to look at hundreds of different stars and compare their patterns.
Bedding hopes each of them will have a different pattern, telling us something about them individually and as a group.