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Colorful stars in the Milky Way contain debris of Earth-like planets

In the debris of two unusually colorful white dwarf stars, astronomers found the remnants of long dead Earth-like planets.

(CN) — The GAIA space observatory of the European Space Agency detected two white dwarfs, locating one at 90 light years away from Earth. Astronomers from the University of Warwick noted that, for the most part, these stars were in a normal state of being. Like the inevitable fate of all stars, their fuel burnt up and their outer layers shed before the stars underwent a process of shrinking and cooling.

To the astronomers’ puzzlement, their study published Friday in Monthly Notices of the Royal Astronomical Society says that one of the dwarfs is unusually blue while the other is the faintest, reddest white dwarf found in the Milky Way.

Abbigail Elms, a PhD student at the University of Warwick's department of physics and lead author of the study, explained via email that white dwarfs follow an evolutionary pattern that mostly remains the same despite some deviations of the usual white color. All except for the two stars of this study.

“The blue white dwarf (WDJ1922+0233) is an outlier, as it is unusually blue for its temperature,” wrote Elms. “The unusual thing about WDJ1922 is that it’s got such a blue color and low temperature for a metal-polluted white dwarf.”

Per the study, the astronomers found that the red star WDJ2147-4035, the one located 90 light years away, spent 10.2 billion years cooling as a white dwarf. It is currently around 10.7 billion years old while the blue star is slightly younger.

The debris of the white dwarfs proved equally interesting.

According to the study, the death of stars disrupts and even destroys orbiting planets, as it will happen to Earth when the Sun dies. Per the astronomers, white dwarfs accrete those pieces, accumulating its mass with the debris of once living planets.

In the debris of the red star, the astronomers found the presence of sodium, lithium, potassium, and possibly detected carbon, making it the oldest metal-polluted white dwarf found so far. The study adds that the debris found in the otherwise nearly pure-helium and high-gravity atmosphere are from an old planetary system that survived when the star evolved into a white dwarf. Because of this, the astronomers say this may be the oldest planetary system around a white dwarf discovered in the Milky Way.

As for the red color, Elms and the team had a theory.

“It is extremely old and has a cool temperature, in addition to it having a vastly different hydrogen to helium atmospheric composition to the other (blue) white dwarf (WDJ1922),” wrote Elms. “WDJ2147 is more helium-rich, so it has less hydrogen molecules in its atmosphere therefore it has less CIA (thus its red optical and near infrared flux is not suppressed nearly as much as in WDJ1922).”

As for the blue star, the study says its color is due to its unusual mixed helium-hydrogen atmosphere. Additionally, Elms revealed that the debris accreted onto the blue star has a composition similar to the Earth’s continental crust.

“There are other planetary systems out there with planetary bodies similar to the Earth. 97% of all stars will become a white dwarf and they’re so ubiquitous around the universe that they are very important to understand, especially these extremely cool ones,” said Elms. “We’re finding the oldest stellar remnants in the Milky Way that are polluted by once Earth-like planets. It’s amazing to think that this happened on the scale of ten billion years, and that those planets died way before the Earth was even formed.”

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