From NASA: “NASA’s Kepler Mission Helps Reveal the Inner Secrets of Giant Stars for the First Time” 

NASA’s Kepler Mission Helps Reveal the Inner Secrets of Giant Stars for the First Time

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“University of Sydney astrophysicists are behind a major breakthrough in the study of the senior citizens of our galaxy: stars known as Red Giants. Using high precision brightness measurements taken by the Kepler spacecraft, scientists have been able to distinguish profound differences inside the cores of stars that otherwise look the same on the surface.

The discovery, published in the latest edition of the journal Nature and made possible by observations using NASA’s powerful Kepler space telescope, is shedding new light on the evolution of stars, including our own sun.

The paper’s lead author, the University of Sydney’s Professor Tim Bedding, explains, ‘ 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.’ “

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Studies of oscillation frequencies of many stars with very high precision gives insights into stellar evolution by knowing how the cores of stars change (starting in the bottom left corner in the sequence above) from hydrogen fusion-burning cores to helium fusion-burning cores, with intermediate stages where hydrogen fusion-burning shells expand into red giant sizes. A Hydrogen shell fusion star and a Helium core fusion star are indistinguishable when looking only at their surface properties. On the inside, they are radically different.
Image credit: Thomas Kallinger, University of British Columbia and University of Vienna

[When you visit the web page, there is a higher resolution image available]

See the full article here.