Stellar X-rays reveal habitability of exoplanets

As the hunt for a habitable planet continues, a team of astronomers have discovered that alot can be learned by studying a star's X-ray emissions.

An artist's illustration showing an older, Sun-like star with a planet in orbit around it. The large dark area is a "coronal hole", a phenomenon associated with low levels of magnetic activity. Inset is an image of one of the subjects of the study: a two billion year old star called GJ 176, located 30 lightyears from Earth. X-ray: NASA/CXC/Queens Univ. of Belfast/R.Booth, et al.; Illustration: NASA/CXC/M.Weiss
Published: September 11, 2017 at 12:00 pm
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Astronomers may be able to learn much about the habitability of exoplanets by analyzing the X-rays emitted from the stars they are orbiting, according to a new study. A team of researchers used data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton to study 24 stars that are similar to our Sun, each one at least one billion years old.

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They studied how the stars’ X-ray brightness changed over time.

The X-rays emitted by stars mirror the magnetic activity of the stars, so studying X-rays can tell astronomers alot about the environment surrounding the star.

The study revealed that stars like the Sun and those that are less massive than the Sun calm down very quickly following a turbulent and energetic youth.

 A tour around GJ 176. X-ray: NASA/CXC/Queens Univ. of Belfast/R.Booth, et al.; Illustration: NASA/CXC/M.Weiss


In order to better understand how the magnetic activity of a star changes over time, scientists require accurate ages for many different stars.

Using studies of how stars pulsate, the team was able to acquire up-to-date age estimates for most of the 24 stars studied.

They found that most stars are very magnetically active when they are young and spin quickly.

As their spin slows, they lose energy and their X-ray emissions drop.

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They observed that older stars settle down relatively quickly, meaning that older, Sun-like stars are more likely to have planets in orbit around them that are suitable for life.

Authors

Iain Todd, BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Staff Writer. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.

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