Sun-like stars calm down after turbulent youth

Sun-like stars and their less massive cousins calm down surprisingly quickly after a turbulent youth, making the atmosphere more suitable for evolution of life, says a new study.

The researchers used data from NASA's Chandra X-ray Observatory and European Space Agency's XMM-Newton to see how the X-ray brightness of stars similar to the Sun behaves over time.

Specifically, the researchers examined 24 stars that have masses similar to the Sun or less, and ages of a billion years or older.

The findings published online in the journal Monthly Notices of the Royal Astronomical Society showed that older stars drop in activity quickly.

The rapid observed decline in X-ray brightness implies a rapid decline in energetic activity, which may provide a hospitable environment for the formation and evolution of life on any orbiting planets.

"This is good news for the future habitability of planets orbiting Sun-like stars, because the amount of harmful X-rays and ultraviolet radiation striking these worlds from stellar flares would be less than we used to think," said lead researcher Rachel Booth from Queen's University in Belfast, Britain.

The X-ray emission from a star comes from a thin, hot, outer layer, called the corona. From studies of solar X-ray emission, astronomers have determined that the corona is heated by processes related to the interplay of turbulent motions and magnetic fields in the outer layers of a star.

High levels of magnetic activity can produce bright X-rays and ultraviolet light from stellar flares.

Strong magnetic activity can also generate powerful eruptions of material from the star's surface.

Such energetic radiation and eruptions can impact planets and could damage or destroy their atmospheres.

Since stellar X-rays mirror magnetic activity, X-ray observations can tell astronomers about the high-energy environment around the star.

The new findings showed that older stars drop in activity far more quickly than their younger counterparts.

To understand how quickly stellar magnetic activity level changes over time, astronomers need accurate ages for many different stars.

This is a difficult task, but new precise age estimates have recently become available from studies of the way that a star pulsates using NASA's Kepler and ESA's CoRoT missions.

These new age estimates were used for most of the 24 stars studied.

--IANS

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