Astronomers find remnants of planets around 10 billion year old stars

November 7, 2022
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Far away in the depths of the Milky Way lie two small, dim stars that are in the final stage of their life. At over 10 billion years old, white dwarfs WDJ2147-4035 and WDJ1922+0233 are among the oldest stars in our galaxy, and recently, astronomers discovered something special orbiting around them: the remains of planets, making this one of the oldest known rocky planetary systems.

Astronomers used data from GAIA, the Dark Energy Survey, and the X-Shooter instrument at the European Southern Observatory to peer at this system. They identified debris from orbiting planetesimals, which are globs of dust and rock which are created during planetary formation. The researchers used spectroscopy to look at the light coming from the two white dwarf stars and break it down into different wavelengths, which can show what materials the stars and the surrounding matter are made of.

Artist’s impression of the old white dwarfs WDJ2147-4035 and WDJ1922+0233 surrounded by orbiting planetary debris, which will accrete onto the stars and pollute their atmospheres. WDJ2147-4035 is extremely red and dim, while WDJ1922+0233 is unusually blue.
Artist’s impression of the old white dwarfs WDJ2147-4035 and WDJ1922+0233 surrounded by orbiting planetary debris, which will accrete onto the stars and pollute their atmospheres. WDJ2147-4035 is extremely red and dim, while WDJ1922+0233 is unusually blue. University of Warwick/Dr Mark Garlick

One of the stars is very red, showing the presence of sodium, lithium, potassium, and perhaps, carbon. The other star is extremely blue, which is caused by its helium and hydrogen atmosphere. The debris around these stars contains metallic elements, which suggest it came from planetary bodies.

“These metal-polluted stars show that Earth isn’t unique, there are other planetary systems out there with planetary bodies similar to the Earth,” said lead author of the study, Abbigail Elms of the University of Warwick, in a statement. “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. Formed from the oldest stars in our galaxy, cool white dwarfs provide information on the formation and evolution of planetary systems around the oldest stars in the Milky Way.”

Studying ancient planetary systems like this one can help astronomers understand how the galaxy has evolved, as metal elements become more abundant over time as they are created by the lifecycle of stars.

“We’re finding the oldest stellar remnants in the Milky Way that are polluted by once Earth-like planets,” said Elms. “It’s amazing to think that this happened on the scale of 10 billion years, and that those planets died way before the Earth was even formed.”

The research is published in the journal Monthly Notices of the Royal Astronomical Society.

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