Vaporized crusts of Earth-like planets are found in dying stars

• Observing lithium and potassium around white stars marks remnants of planetary rocky crusts
• A study by astronomers led by the University of Warwick shows that the chemical combination of crusts is very similar to Earth’s continental crust.
• The outer layers of the white dwarfs contain up to 300,000 gigatonnes of rocky debris, which contains up to 60 gigatonnes of lithium and 3,000 gigatonnes of potassium.
• These white dwarfs are among the oldest stars in our galaxy, and could host one of the oldest planetary systems discovered to date.

Remnants of planets with Earth-like crusts have been discovered in the atmosphere of four nearby white stars by University of Warwick astronauts, offering a view of the planets that may have been moved up billions of billions ago.

These crusts are from the outer layers of rocky planets like Earth and Mars and could give astronomers more insight into the chemistry of the planets that these dying stars hosted.

The findings are reported today (February 11) in the journal Astronomy of nature and it includes one of the oldest planetary systems seen by astronauts to date.

The team led by the University of Warwick was analyzing data from the European Space Agency’s Gaia telescope of more than 1,000 nearby white dwarf stars when they came across a strange signal from one particular white dwarf. The researchers at the University of Warwick received funding from the European Research Council and the Science and Technology Resources Council (SCFC).

They used spectroscopy to study the light from the star at different waves, which allows them to find out when elements in the star’s atmosphere absorb light at different colors and determine what the elements are and to what extent they are present. They also examined the 30,000 white glasses from the Sloan Digital Sky Study published over the past 20 years.

The signal matched a lithium wave and the astronomers soon discovered three more white dwarfs with the same signal, and potassium in the atmosphere was also seen. By comparing the contents of lithium and potassium with the other elements they found – sodium and calcium – they found that the ratio of elements matched the chemical composition of the crust of the rocky planets as Earth and Mars, if these crusts and were damaged and mixed within gaseous layers outside the star for 2 million years.

Lead author Dr Mark Hollands from the University of Warwick ‘s Department of Physics, said: “In the past, we’ve seen all sorts of things like clothing and materials, but we haven’t found a definitive trace of planetary crust. Lithium and potassium are good indicators of bark products, they are not present in high concentrations in the healthy or heart.

“Now that we know what chemical signature we are looking for to find these elements, we have the opportunity to look at a large number of white terriers and find more of these. Then we can look at the orbit of that signature and see how often we find these planetary crusts and how that compares to what we are predicting. “

The outer layers of the white dwarfs contain up to 300,000 gigatonnes of rocky debris, which contains up to 60 gigatonnes of lithium and 3,000 gigatonnes of potassium, equivalent to an area of ​​60km of equal density. to the Earth’s crust. The amount of crusting material found is similar in mass to the asteroids we see in our own solar system, leading astronomers to believe that what they see around the four stars as material broken away from a planet, rather than an entire planet. yourself.

Previous studies of white dwarfs have found evidence of material from the inner core and costumes of planets, but there is no conclusive evidence of bark. A fragment is a small fraction of planetary ornamentation and the elements found in this study can only be detected when the star is very cool. White dwarfs are in the dying stage of their life cycle, as they have burned and cooled the fuel over billions of years. These four white dwarfs are thought to have burned their fuel up to 10 billion years ago and could be among the oldest white dwarfs created in our galaxy.

Co-author Dr Pier-Emmanuel Tremblay from the University of Warwick said: “In one case, we are looking at the creation of a planet around a star created in the Galactic Halo, 11-12.5 billion years ago, and as that this must be one of the oldest known planetary systems to date.Another of these systems created around a short-lived star that was initially more than four times the mass of the sun, a discovery that was less successful deliver important constraints on how fast planets can form around their host stars. “

Among the oldest of these white dwarfs, one is 70% larger than average so its large mass would normally remove any substance in its atmosphere relatively quickly, which forcing the astronauts to conclude that it needs to refill the crust material from its surrounding debris disk. In addition, the astronauts detected more infrared light than expected for the white dwarf alone, which shows a disk heated by the star and then re-radiating at longer waves.

Dr Hollands said: “As we understand it, the formation of a rocky planet occurs in the same way in different planetary systems. First, they are formed from the production of star-like materials, but over time. these substances separate and you end up with different chemical decisions.In different parts of the planets.We will see at some point that these things have gone through differentiation, where whether the combination is different from the starting position of the star.

“It is now understood that most normal stars are like solar port planets, but now there is an opportunity to look at the frequency of different types of materials as well.”

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* ‘Alkaline metals in white atmospheres as finders of ancient planetary crusts’ will be published in Astronomy of nature, DOI: 10.1038 / s41550-020-01296-7
Connection: https: //www.nature.com /articles /s41550-020-01296-7

* This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant agreement No. 677706 (WD3D))

Notes to Editors:

An artist’s impression of planetary crusts assembled into a white version available for download at the link below. This image is free to use if used in direct connection to this story but University of Warwick / Mark Garlick image copyright and credibility requires:
https: //warwick.ac.uk /services /communication /medialibrary /images /February_2021 /accreting_wd2.jpg

Caption: The remnants of a planet’s crust sinking beneath the tidal forces around a cool white dwarf. Material in the disk becomes vaporised near the star in the center and flows into the bright white atmosphere. Credit: University of Warwick / Mark Garlick

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