It’s easy to forget our place in the universe, but planets have been born, lived and died long before Earth even existed. Now astronomers have detected the ruins of ancient planets around two unusual white dwarf stars, including an Earth-like world that existed almost 10 billion years ago.
When most stars, including our Sun, run out of hydrogen to burn, they swell up into a red giant, then eventually shed their outer layers and leave behind a dense core, known as a white dwarf. Any planets that may have been orbiting the original star would have a hard time surviving this process, and their remnants can be detected falling into and “polluting” the white dwarf.
In a new study, astronomers examined data on two strange white dwarfs, including one that’s unusually blue and another that’s fainter and redder than most. Studying the light from these stars can reveal how old they are, as well as what elements are burning up in their atmospheres, which by extension can reveal the makeup and type of the planets they used to host.
The blue white dwarf, known as WD J1922+0233, was found to have formed about nine billion years ago, meaning its planets existed and faced their apocalypse before that. The star’s light revealed that the planetary debris had a composition similar to Earth’s continental crust.
The redder white dwarf, known as WDJ2147-4035, is just 90 light-years away and was found to be about 10.7 billion years old, becoming a white dwarf around 10.2 billion years ago. Its light analysis revealed a strange mix of elements from its planetary debris, including sodium, lithium and potassium. It’s also the coldest white dwarf detected so far, with a surface temperature of just 2,777 °C (5,030 °F).
“The red star WDJ2147-4035 is a mystery as the accreted planetary debris are very lithium and potassium rich and unlike anything known in our own solar system,” said Abbigail Elms, lead author of the study. “This is a very interesting white dwarf as its ultra-cool surface temperature, the metals polluting it, its old age, and the fact that it is magnetic, makes it extremely rare.”
The team says this is the oldest known planetary system around a white dwarf in our galaxy. For reference, both of these white dwarfs are more than twice the age of our own solar system.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.
Source: University of Warwick