Discovery of lithium-rich star to shed new light on evolution of universe

CHINESE astronomers have discovered the most lithium-rich giant star ever known, which could shed new light on the evolution of the universe.

With 3,000 times more lithium than a normal star, it was found in the direction of Ophiuchus, on the north side of the galactic disk, at a distance of 4,500 light years from Earth.

A research team, led by astronomers from National Astronomical Observatories of China (NAOC) of the Chinese Academy of Sciences, made the discovery with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), a special quasi-meridian reflecting Schmidt telescope located in NAOC’s Xinglong Observatory, in north China’s Hebei Province.

The telescope can observe about 4,000 celestial bodies at one time and has made a massive contribution to the study of the structure of the galaxy.

Lithium is considered one of the three elements synthesized in the Big Bang, together with hydrogen and helium. The abundance of the three elements was regarded as the strongest evidence of the Big Bang.

The evolution of lithium has been a key subject in the research of the evolution of the universe and stars. However, giant stars rich in lithium are very rare, with only a few found over the past three decades. This makes their study remarkably challenging, said Zhao Gang, a lead astronomer at NAOC.

“The discovery of this star has largely increased the upper limit of observed lithium abundance,” said Zhao.

The newly discovered star has a mass almost 1.5 times the sun. Details of the star were obtained by follow-up observation through the Automated Planet Finder telescope at Lick Observatory in the United States.

Scientists from other institutions, including the China Institute of Atomic Energy and Beijing Normal University, joined the team and helped discern a possible explanation for the lithium-rich phenomenon through a nuclear network simulation with the latest atomic data.

The researchers believe the abundant lithium might be a result of a special material exchange process in the interior of the star.

Finished in 2008, LAMOST began regular surveys in 2012. It has helped Chinese scientists with a final catalogue of about 10 million spectra over six years and established the world’s largest databank of stellar spectra.

“The number of stellar spectra released by LAMOST is 1.8 times more than the total of other astronomic surveys,” said Zhao.

Spectra are key for astronomers to read celestial bodies’ chemical compositions, densities, atmospheres and magnetism.

With LAMOST, astronomers have found the Milky Way could be twice as wide as previously thought. They also have a clearer picture of the structure of the halo around the galaxy, and new evidence that it was formed by merges of small galaxies.

Using data from the telescope, they estimated that dark matter makes up over 90 percent of the total mass in our galaxy. But the density of dark matter is low in the location of the sun, which makes it very difficult to detect dark matter directly. The telescope can also help calculate the age of more than a million stars, providing basic data to study the evolution of our galaxy.

Astronomers measured the magnetic activity index of about 6,000 sun-like stars, as well as the eccentricity and inclination angle of the orbits of about 700 exoplanets, and found that almost 80 percent of their orbits are near circular, similar to the orbits of planets in the solar system.

This indicates the solar system is not special in the universe, giving scientists more confidence in the search for Earth-like exoplanets and extraterrestrial life.

From the spectra collected by LAMOST, astronomers have discovered some unusual stars. For instance, five “hypervelocity stars” which travel fast enough to escape the gravitational grasp of the Milky Way have been found.

Astronomers have also discovered more than 12,000 quasars at the far reaches of the universe.