A new study by astronomers has shed light on new light on the evolution of stars, including our own sun.

NASA's Kepler spacecraft helped scientists to distinguish profound differences inside the cores of stars that otherwise look the same on the surface. Kepler Mission is a NASA program supported by a space observatory - the Kepler spacecraft - designed to discover Earth-like planets orbiting other stars.

With findings from Kepler, astrophysicists at University of Sydney have struck a major breakthrough in the study of the senior citizens of our galaxy: stars known as Red Giants.

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores that powers nuclear fusion, and instead burn hydrogen in a surrounding shell. Towards the end of their lives, red giants begin burning the helium in their cores, University of Sydney's Professor Tim Bedding said in a statement.

The changes in brightness at a star's surface is a result of turbulent motions inside that cause continuous star-quakes, creating sound waves that travel down through the interior and back to the surface, Professor Bedding said.

Under the right conditions, these waves interact with other waves trapped inside the star's helium core. It is these 'mixed' oscillation modes that are the key to understanding a star's particular life stage.

By carefully measuring very subtle features of the oscillations in a star's brightness, scientists found that some stars have run out of hydrogen in the center and are now burning helium, and are therefore at a later stage of life.

As a star burns hydrogen in fusion reactions, helium builds up in the star's core. Helium is denser than hydrogen, and since waves travel more quickly through denser material, waves travel faster through the core as helium builds up there.

Professor Bedding and his colleagues work in an expanding field called asteroseismology. In the same way that geologists use earthquakes to explore Earth's interior, we use star quakes to explore the internal structure of stars, he explained.

Professor Bedding said: We are very excited about the results. We had some idea from theoretical models that these subtle oscillation patterns would be there, but this confirms our models. It allows us to tell red giants apart, and we will be able to compare the fraction of stars that are at the different stages of evolution in a way that we couldn't before.

The discovery was published in the latest edition of the journal Nature.