Kepler Spacecraft Penetrates Secrets of Red Giant Stars -Habitable Zones for Life

  Redgiant

NASA's Kepler Planet-Hunting Mission is providing astronomers with an inside view of what's happening inside red giant stars. "No one anticipated seeing this before the mission launched," said Steve Kawaler, an Iowa State University professor of physics and astronomy and a leader of the Kepler Asteroseismic Investigation. "That we could see so clearly down below a red giant star's surface was unexpected."

One reason for studying red-giant stars is to understand how their habitable zones move farther out as the star's radiating surface becomes bigger. Based on how long it took for life to develop on Earth, scientists speculate that there is more than enough time during a star's giant phase for life to get a start somewhere in the evolving habitable zones.


"In our solar system, places like Europa – a satellite of Jupiter that now is covered by a thick layer of water ice — might warm up enough to support life for more than a billion years or so, over the time when our Sun begins to evolve into a red giant, making life on Earth impossible," according to  Penn State's Alex Wolszczan, who in 1992 discovered the first planets ever found outside our solar system.

Another reason astronomers are trying to discover planets around different kinds of stars at different stages of stellar evolution is to find out how different kinds of planetary systems change when their stars become red giants and how they ultimately end their lives as burnt-out, shrunken white-dwarfs.

New papers describe how Kepler tracks tiny, regular changes in star brightness. Their regularity resembles steady drumbeats at different, precise rhythms. Each rhythm can be thought of as an individual tooth of a comb. Astronomers have studied those oscillations from ground-based telescopes to determine star basics such as mass and radius. But they noticed departures from the steady patterns in the Kepler data-breaks in the combs, caused by gravity mode oscillations that allow researchers to probe a star's core and gather data about the density and chemistry deep inside a star.

And for the first time the data also shows researchers whether a red giant star burns hydrogen in a shell surrounding the star or whether it has evolved to an age that it burns helium in the core.

"The stars burning helium in the core survived a helium flash," Kawaler said. "That transformation from stars burning a hydrogen shell is mysterious. We think it happens quickly and perhaps explosively. Now we can tell which stars have done that and which stars will do that."  

The Kepler findings will assist astronomers in understanding the life cycle of red giant stars. Our sun will evolve into a red giant in about 5 billion years.

Kepler launched March 6, 2009, continually pointed at the Cygnus-Lyra region of the Milky Way galaxy. Its primary job is to use tiny variations in the brightness of the stars within its view to find earth-like planets that might be able to support life.

The Daily Galaxy via Iowa State University

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