Remains of oldest known solar system discovered 90 light-years from Earth
The oldest dead star known to have possessed a system of rocky planets has been discovered just 90 light-years from Earth and provides insight into the makeup of worlds formed nearly 11 billion years ago.
The star is a so-called white dwarf, a stellar corpse that ran out of hydrogen fuel at its core. Born as a normal star 10.7 billion years ago (just 3 billion years after the big bang), the stellar corpse, named WDJ2147-4035, is one of two white dwarfs polluted by planetary debris recently discovered in data collected by the European Space Agency’s Gaia galaxy mapping mission.
Although they are not the first white dwarfs found to collect debris from an apparent planetary demolition derby, they are the oldest and therefore offer a keen insight into the composition of planets that formed when the universe was less than 3 billion years old.
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In the case of WDJ2147-4035, its ancestor was more massive than the sunbut not massive enough to explode like a supernova at the end of his life. Instead, half a million years after its formation, or about 10.2 billion years ago, the star ran out of fusion hydrogen at its core and swelled to become a star. red giant. It then puffed off its outer layers to expose its inert helium-rich core — a white dwarf.
While the gravitational fields were in motion as the star evolved through its red giant phase, some of the planets in orbit were destroyed or disrupted, while others may survived intact. Regardless, the disturbances resulted in large amounts of planetary debris that has since fallen on the white dwarf.
Astronomers led by Abigail Elms, a PhD student at the University of Warwick in the UK, used measurements of light spectra from Gaia, the Dark Energy Survey using the Dark Energy Camera on the Victor M. Blanco Telescope of the Cerro Tololo Inter-American Observatory in Chile, and the X-Shooter instrument of the Very Large Telescope also in Chile, to analyze the chemical composition of the red-colored WDJ2147-4035, and the second white dwarf, WDJ1922+0233, which appears blue.
The results show a surprising diversity of planetary compositions. Blue WDJ1922+0233, which owes its color not to temperature but to the unusual mixing of gases in its helium-hydrogen atmosphere, is apparently polluted by material similar in composition to that of the Earth’s continental crust.
“These metal-polluted stars show that the Earth is not unique, [that] there are other planetary systems with planetary bodies similar to: Soil,” said Elms in a pronunciation (opens in new tab).
The red WDJ2147-4035 is more of a puzzle. It will be enriched with lithium, potassium, sodium and a preliminary detection of carbon accreting on the white dwarf.
“The red star WDJ2147-4035 is a mystery, as the accumulated planetary debris is very lithium and potassium rich and unlike anything known in our own solar system,” Elms said.
Regardless, the findings provide further evidence that rocky planets could form in abundance in the distant past, despite heavy elements being less common in the universe at that time, because those elements had to be built up by each generation of stars.
“It’s amazing to think that this happened on a 10-billion-year scale, and that those planets died long before Earth even formed,” Elms said.
The research (opens in new tab) was published in the November 5 issue of Monthly Notices of the Royal Astronomical Society.
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