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China science

Chinese scientists discover lithium-rich star that could help explain how the universe evolved

A giant star located 4,500 light years from Earth offers new clues for astrophysicists

PUBLISHED : Tuesday, 07 August, 2018, 10:00pm
UPDATED : Wednesday, 08 August, 2018, 1:30am

Chinese scientists have discovered the most lithium-rich giant star ever known, which could shed new light on how the universe evolved.

The new discovery has 3,000 times as much lithium as the sun yet its mass is just 50 per cent greater, astronomers from the National Astronomical Observatories of China (NAOC) said in a study published on Monday in the scientific journal Nature Astronomy.

The unnamed star is a rarity – only one per cent of giant stars are lithium-rich – and located in the direction of the constellation Ophiuchus, northwest of the centre of the Milky Way, about 4,500 light years from Earth, the study said.

It was discovered by analysing images captured by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope in northern China.

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The telescope, which has conducted regular surveys of the night sky since 2012, has helped scientists assemble the world’s largest database of celestial spectra, about 10 million images.

Astronomers use the images to determine the composition of stars.

“Lithium is one of the key elements that connects the Big Bang, the interstellar medium and stars,” said Yan Hongliang, an assistant research fellow with the NAOC and a lead scientist on the study.

“The evolution of lithium has been widely studied in modern astrophysics, but our understanding of it is still quite limited.”

The Big Bang model is the widely held theory of how the universe came into being and subsequently evolved, expanding from a highly compressed state to what exists today over 13.8 billion years.

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Lithium is a silvery white metal with the atomic number 3, one of the earliest elements in the universe. Along with hydrogen and helium, it was created during the Big Bang.

Thus, lithium is considered an elemental marker of early cosmic evolution. Lithium-rich stars were first discovered by the American astronomers George Wallerstein and Chris Sneden in 1982.

The metal is widely used in electronics. Lithium batteries power mobile phones, laptops, electronic vehicles and drones.

Yan said that he and his team were surprised to find the star contained such a large amount of lithium in relation to its age. A giant star, thought to represent an intermediate state in the evolution of a star, generally holds only small amounts of lithium, he said, since the element ought to have been consumed in the sun’s earlier stages.

Determining why a relatively old star has higher-than-expected lithium will provide new information about the aging process of stars. At a minimum, Yan said, this discovery is likely to help decode the evolution of lithium in stars.

One hypothesis is that this giant star swallowed its planet – like the sun consuming the Earth – and absorbed its lithium, Yan said.

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Another hypothesis suggests that lithium formed inside the giant star and reached the surface before the high temperature in the star’s deepest layers vaporised it.

“It is still too soon to draw any firm conclusions,” Yan said.

“There are some hints that the lithium-rich phenomenon might be due to more than one scenario.”