Remains of asteroids in a white dwarf star could help astronomers find “missing” lithium

Crushed asteroids found in the atmosphere of a long-dead white dwarf star could help astronomers find and measure the universe’s missing lithium.

Lithium measurements in stars like our Sun have never been added to the amount that scientists predict should exist – suggesting that there is much more than we can find.

The Big Bang, the main explanation for how the universe began 13.8 billion years ago, produced three elements: hydrogen, helium and lithium.

Of the three elements, lithium is the greatest mystery. But the new study by astronomers at the University of North Carolina provides clues to its evolution.

Finding traces of the element in the rocky remains of an asteroid in the atmosphere of a nine-billion-year-old white dwarf could help scientists estimate the total amount of lithium in the universe, as it suggests that it may be scattered in rocky bodies.

It is the first time the hard-to-find element has been identified in the burnt remains of a dead star, according to researchers at the University of North Carolina.

Despite its many uses on Earth to power electronics and stabilize moods, scientists have been surprised by what has become expected of the Big Bang lithium, a discrepancy known as the “cosmological problem of lithium.”

No one knows exactly how much lithium there is in the universe, but these new discoveries mean that white dwarf stars could be used to estimate the total amount.

The discovery was made possible by using a unique spectrograph mounted on the Southern Astrophysical Research telescope.

The study’s author, astrophysicist J. Christopher Clemens, led the design of the Goldman spectrograph, which measures how much light is emitted by a white dwarf.

White dwarfs are the remaining nuclei that remain when the stars die and can be surrounded by rocky worlds. Our sun will become a white dwarf when it dies.

The high gravity of the surface of these stars should cause elements heavier than hydrogen and helium to sink rapidly beneath the surface.

However, some “polluted” white dwarf stars show evidence of heavier elements on their surfaces, believed to be due to recent accumulations of rock bodies.

In the study, the researchers describe the detection of the crushed remains of large asteroid-like objects in the atmosphere of two very old white dwarfs.

The planets of these dead stars first formed nine billion years ago – our sun and planets formed only 4.6 billion years ago.

The team measured the chemical composition of asteroids and, for the first time, identified and measured both lithium and potassium in an extrasolar rock body.

The theory predicts that lithium formed especially in the first five minutes after the Big Bang. Its later history is different from other elements and is more uncertain, because lithium is consumed by nuclear reactions in stars.

Finding it in white dwarf stars provides evidence of the original rocky bodies that formed nine billion years ago – and therefore the galactic abundance of lithium at the time they formed – in the first few billion years of the universe. .

The authors note that the accumulated bodies, such as those that polluted this star, are an alternative to the old stars to get a perspective on the primordial. [lithium] abundance, the first epochs of chemical enrichment in our galaxy and the properties of ancient exoplanets. ‘

“Measuring lithium from a rocky body in another solar system lays the groundwork for a more reliable way to track the amount of lithium in our galaxy over time,” Clemens said.

“Finally, with enough of these white dwarfs that had asteroids falling on them, we will be able to test the prediction of the amount of lithium formed in the Big Bang.

The findings were published in the journal Science.