Scientists have discovered one of the oldest star systems with rocky planets in our galaxy, two white dwarf stars and the remains of rocky planets over 10 billion years old.
Stars like our Sun eventually consume most of their thermonuclear fuel, first swelling into a large red giant star, then shrinking and cooling into a small white dwarf star.
Researchers at the University of Warwick have discovered two white dwarf stars about 90 light-years from Earth whose light changes color due to material from ancient rocky planets, likely destroyed by the red giant phase stars, falling into the two stars. The slightly reddish white dwarf star WDJ2147-4035 is about 10.7 billion years old, according to a paper published Saturday in the Royal Astronomical Society Monthly Noticeswhile a second bluish star, WDJ1922+0233, is just slightly younger.
“We find the oldest stellar remnants in the Milky Way that are polluted by once-Earth-like planets,” Abbigail Elms, a PhD student in physics at the University of Warwick and lead author of the study, said in a statement. “It’s amazing to think that this happened on the scale of ten billion years, and that these planets died long before Earth was even formed.”
The researchers first identified the two stars using the European Space Agency’s Gaia space observatory. They then used the European Southern Observatory’s X-Shooter spectrography instrument to analyze starlight to measure the materials in those stars.
The reddish star WDJ2147-4035 has shown signs of sodium, lithium, potassium, and possibly carbon pollution from the remnants of planets surrounding the star.
“The red star WDJ2147-4035 is a mystery because the accumulated planetary debris is very rich in lithium and potassium and unlike anything known in our own solar system,” Elms said. “It is a very interesting white dwarf because its ultra-cold surface temperature, the metals that pollute it, its old age and the fact that it is magnetic, make it extremely rare.”
The bluish star WDJ1922+0233 seems to be polluted by materials much closer to the Earth’s crust in their composition.
“These metal-polluted stars show that Earth is not unique, there are other planetary systems with planetary bodies similar to Earth,” Elms said, adding that stars on the same life course as our Sun, destined to become white dwarfs, are also not unique. “Formed from the oldest stars in our galaxy, cool white dwarfs provide insight into the formation and evolution of planetary systems around the oldest stars in the Milky Way.”