Remains of asteroids inside a white dwarf star could help astronomers find ‘missing’ lithium

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

Lithium measurements in stars like our own sun have never added to the amount scientists say should exist – suggesting 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 presents the greatest mystery. But the new study by University of North Carolina astronomers provides clues to track 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 it could spread to rocky bodies .

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

Despite the many uses on Earth to power electronics and stabilize moods, scientists are dumbfounded at what happened to the lithium expected from the Big Bang, a discrepancy known as the ‘cosmological lithium problem’.

No one knows exactly how much lithium is in the universe, but these new findings mean that white dwarf stars can be used to estimate the total number.

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

Study author, astrophysicist J. Christopher Clemens, led the design of the Goldman spectrograph that measures how much light is emitted by a white dwarf.

White dwarfs are the leftover cores that are left when stars die, and they can be surrounded by rocky worlds. Our sun will become a white dwarf when it dies.

Due to the high gravity of these stars, elements heavier than hydrogen and helium should quickly sink below the surface.

Nevertheless, some ‘polluted’ white dwarf stars show evidence of heavier elements on their surfaces, presumably the result of recent growth of rocky bodies.

In the study, researchers describe detecting 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 the planets formed only 4.6 billion years ago.

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

Theory predicts that lithium was largely formed in the first five minutes after the Big Bang. Its later history differs from other elements and is more uncertain because lithium is consumed by nuclear reactions in stars.

Finding it in the white dwarf stars will give you an overview of the original rocky bodies that were formed nine billion years ago – and thus the galactic abundance of lithium at the time they were formed – in the universe’s first few billion years .

The authors note that accrued bodies such as those that polluted this star “ are an alternative to old stars to gain insight into the original [lithium] abundance, the earliest eras of chemical enrichment in our Milky Way, and the properties of ancient exoplanets. ‘

“Our measurement of lithium from a rocky body in another solar system lays the groundwork for a more reliable method of tracking the amount of lithium in our galaxy over time,” said Clemens.

With enough of these white dwarfs that have fallen asteroids, we can test the prediction of the amount of lithium formed in the Big Bang.

The findings are published in the journal Science.