Violent seismic shakes reveal red giant secrets

Becoming a swollen red giant is the future of our sun when it begins to exhaust its fuel on its way to death. Recently, data from the hardworking Kepler telescope recorded seismic shakes or "starquakes" on the surface of a red giant that led to the intriguing discovery their cores spin faster than their surface.

Scientists know as red giants die, their cores become dense and contract and the outer surfaces expand and cool. They had theorized the cores spun faster as they contracted — in a similar fashion as an ice skater who spins faster as they draw their arms closer.

The starquakes have validated this theory, with data showing the centers likely spin at least 10 times faster than the surface. This knowledge helps scientists further understand red giants and other stars in their life cycle, and has birthed a new field of "astroseismology."

Starquakes are caused by the stars' violent quaking, generating rippling sound waves that can be "seen" as rhythmic variations in the brightness of the star. Researchers used NASA's Kepler spacecraft and ground based telescopes to focus on three red giants over 500 days. They recorded the vibration linked ripples in the brightness of the stars to calculate how the cores were spinning.

Scientists calculated the spin rates by looking at the footprint of elements in the stars — represented by black lines in the spectrum of light in the various wavelengths we see emitted from the surface. As the stars rotate, changes in the rippling light spectrum reveal the speed when viewed in relation to the black bands.

Fortunately for us, there are astroseismologists who are beginning understand these spinning red behemoths. That leaves us regular space nuts to marvel at how a star can spin at two different speeds — and breathe a sigh of relief that our sun won't become a red giant for some five billion years. Phew!


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