The life of a main-sequence star like the Sun might not end with a supernova like more massive stars, but it wouldn’t be a quiet affair.
When the star runs out of fuel and becomes unstable, it swells to an extremely massive size before exploding from its outer material while the core collapses into a tiny, extremely dense white dwarf.
For the Sun, that red, bulging giant phase could extend to Mars, a process that can destabilize and destroy planets close enough.
We’ve seen white dwarf stars that have planets, indicating that they can survive the process (or form after). But, increasingly, scientists have discovered that many exoplanets are devoured by the white dwarf.
We can find out because of the “pollution” that planetary elements cause in the atmosphere of white dwarf stars, the study of which is known as dead planetology.
And now, astronomers have discovered the oldest known example: an exoplanet devoured by a white dwarf that formed 10.2 billion years ago.
About 90 light-years from Earth, the white dwarf is incredibly small and faint, with a more unusual red color than any other white dwarf star. A second white dwarf star, unusually blue, formed 9 billion years ago. The team found that both stars face constant pollution by inundating planetary debris.
However, while the red star, called WD J2147-4035, represents the oldest polluted white dwarf discovered to date, the blue star, called WD J1922+0233, is probably more interesting: elements in its atmosphere suggest that The star is eating a planet very similar to Earth.
“We find the oldest stellar remnants in the Milky Way that are contaminated with Earth-like planets,” says astrophysicist Abigail Elms from the University of Warwick in the UK. “It’s amazing to think that this happened on a 10-billion-year scale and that those planets died before Earth was even formed.”
We can dissect the chemical composition of a star’s atmosphere from the light emitted by the star. Not all wavelengths are emitted equally: some are stronger, some are weaker. This is because the elements can absorb and re-emit light, changing the spectrum of light coming out of the star.
It’s not immediately clear which elements play a role, but scientists are getting better at identifying the absorption and emission features on the spectrum associated with the elements.
When the European Space Agency’s Gaia space observatory identified the unusually colored white dwarfs, Elms and her colleagues subjected the two strange spheres to various studies.
Because white dwarf stars no longer function by fusion of elements in their cores, their temperatures are slowly decreasing at a known rate; By measuring the temperatures of the two stars, the researchers were able to measure how long it had been since their formation from the death of a Sun-like star.
Next, they subjected the stars’ spectra to analyzes to determine their atmospheric compositions. On the red star, they find sodium, lithium, potassium, and possibly carbon. On the blue star they find sodium, calcium and potassium.
Since white dwarfs are so gravitational, heavy elements like this should disappear into the white dwarf’s interior, undetectable, and very quickly; This indicates that the material that produces these elements is still falling on the stars from the clouds of debris around them.
In the case of WD J2147-4035, the team determined that the pollution might have been the remnants of a planetary system that orbited the star before it died, survived the throes of stellar death, and is now slowly falling over billions of years. The star.
Since the star turned into a white dwarf more than 10 billion years ago, this makes it the oldest known planetary system in the Milky Way (although it has broken up and disappeared).
Meanwhile, the contaminated debris of WD J1922+0233 has a makeup similar to Earth’s continental crust, suggesting an Earth-like planet orbiting a sun-like star that lived and died billions of years before the solar system formed.
It’s like the galactic fossil record that can tell us what the planetary systems of the Milky Way were eons before we got here to marvel at its wonders.
“When these ancient stars formed more than 10 billion years ago, the universe was less metal-rich than it is now, with minerals forming in advanced stars and giant starbursts,” says astrophysicist Pierre-Emmanuel Tremblay of the University of Warwick.
“The observed white dwarfs provide an interesting window into planet formation in a mineral-poor, gas-rich environment that was different from conditions when the solar system formed.”
The search was published in Monthly Notices of the Royal Astronomical Society.