When our Sun reaches the end of its life, it will first begin to grow exaggeratedly. Then it will shrink. Transforming into a white dwarf. What will then become of these planets that make up our solar system today? Astronomers hope to find out by studying other planetary systems elsewhere in the Milky Way. And today for the first time, they report observing the debris of an exoplanet being swallowed up by the remains of its star.
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[EN VIDÉO] Exoplanets What are exoplanets, where are they found and why are they so interesting? Video answer!
In the theater of some 5,000 confirmed exoplanets, there are sometimes dramas. It happens that some planets are disintegrated by their own star. Especially when the latter, having reached the end of its life, begins to swell to become what the astronomers call a red giant. It is moreover what will happen to our Sun within 5 billion years. At that time it will swallow up Mercury and Venus. Maybe also our Earth.
Once the process is complete — count about a billion years for a star in the mass of ours –, the volume of the dying star decreases again. Until it becomes a white dwarf. White dwarfs, there are at least 300,000 in the world alone. Milky Way. And their story suggests to researchers that these already formidably dense star remnants accrete all sorts of debris from planets or other objects that orbited them when they were still living stars.
For several decades now, astronomers have been scrutinizing white dwarfs at wavelengths optical and ultraviolet. Relying on spectroscopy to determine the composition of these star remnants. And as indirect evidence that these objects tend to swallow debris from planets, they have some traces ofheavy elements — iron, calcium or magnesium from sunken planets — over a quarter of white dwarfs.
The fate that awaits our solar system
Researchers from the University of Warwick (UK) went further. They finally managed to literally see debris from exoplanets falling into theatmosphere of a star. That of G29-38, in the constellation of Pisces.
To do this, they explored the field of X-rays. Because when matter is attracted to a star at a speed large enough and hits its atmosphere, a plasma is formed whose temperature is between 100,000 and 1 million Kelvin. As it cools, it emits X-rays. Which arrive in small quantities to our Earth.
It is thanks to the great resolution angularChandra X-ray Space Observatory (Nasa) that astronomers were able to isolate G29-38 from surrounding sources. And observe, for the first time, how the debris of a exoplanet shattered into a thousand pieces are piling up on the white dwarf that was once its host star. The opportunity already to confirm that the rate ofaccretion calculated here agrees extremely well with that deduced from spectroscopic measurements and models of white dwarfs.
The researchers now hope to succeed in observing more exoplanets ending up in their star. In order to better understand the fate that awaits thousands of planetary systems. Among which, ours!
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