Scientists may have discovered one of our galaxy’s oldest star systems with rocky planets, two white dwarf stars, and the remains of rocky planets dating back more than 10 billion years.
Stars like our Sun eventually deplete their thermonuclear fuel, first expanding into a large red giant star and then contracting and cooling into a smaller white dwarf star.
Researchers at the University of Warwick discovered two white dwarf stars about 90 light years away from Earth, whose light is changing colour due to material falling into the stars from former rocky planets, which were likely destroyed by the stars’ red giant phase. According to a paper published Saturday in the Monthly Notices of the Royal Astronomical Society, the slightly reddish WDJ2147-4035 white dwarf star is about 10.7 billion years old, while a second blueish star, WDJ1922+0233, is only slightly younger.
“We’re discovering the oldest stellar remnants in the Milky Way that have been polluted by once Earth-like planets,” said Abbigail Elms, a PhD student in physics at the University of Warwick and the study’s lead author. “It’s incredible to think that this happened over ten billion years, and that those planets died long before the Earth was formed.”
The two stars were discovered using the European Space Agency’s Gaia space observatory. The European Southern Observatory’s X-Shooter spectrography instrument was then used to analyse the light of the stars in order to determine what materials were present in those stars.
The reddish star WDJ2147-4035 has shown signs of being polluted by sodium, lithium, potassium, and possibly carbon from planet remnants.
“The red star WDJ2147-4035 is a mystery because the accreted planetary debris is very lithium and potassium rich, unlike anything known in our own solar system,” said Ms Elms. “This is a very interesting white dwarf because of its ultra-cool surface temperature, the metals polluting it, its age, and the fact that it is magnetic.”
The blueish star WDJ1922+0233 appears to be polluted by materials that are much more similar in composition to Earth’s crust.
“These metal-polluted stars show that Earth isn’t unique; there are other planetary systems out there with planetary bodies similar to Earth,” Ms Elms said, adding that stars on the same lifecourse as our Sun, destined to become white dwarfs, aren’t either. “Cool white dwarfs, formed from the oldest stars in our galaxy, provide information on the formation and evolution of planetary systems around the Milky Way’s oldest stars.”