Ancient Star Rich In Oxygen Offers Clues On Elements Produced By The First Stars

ARTISTIC IMAGE OF THE SUPERNOVA EXPLOSIONS OF THE FIRST MASSIVE STARS THAT FORMED IN THE MILKY WAY. THE STAR J0815+4729 WAS FORMED FROM THE MATERIAL EJECTED BY THESE FIRST SUPERNOVAE. Gabriel Pérez Díaz, SMM (IAC)

An international team of astronomers has discovered that there are large quantities of oxygen in the atmosphere of one of the oldest known stars, a fact that informs us about what kind of material this particular object formed from.

The observations of “primitive star” J0815+4729 are reported in The Astrophysical Journal. The number of elements these stars possess is a window into the past. The first stars that ever formed in the universe were made only of hydrogen and helium. Once they went supernova, they enriched surrounding hydrogen with heavier elements such as carbon and oxygen, and from those hydrogen clouds, new stars formed.

J0815+4729 is among those second generation of stars. We are yet to see stars from the first population, but from studying this object and the heavy elements present in it, we can gain important insights into what came before. The team believes that the pre-stellar cloud of J0815+4729 was enriched by a supernova between 21 and 27 times the mass of the Sun.

J0815+4729 is located in the galactic halo, the spherical region around the Milky Way’s thin disk, where the Sun and the stars make up the spiral arms. It is located 5,000 light-years towards the constellation Lynx.

“The primitive composition of the star indicates that it was formed during the first hundreds of millions of years after the Big Bang, possibly from the material expelled from the first supernovae of the Milky Way,” lead author Dr Jonay González Hernández from the Instituto de Astrofısica de Canarias, said in a statement.

The observations were possible thanks to the W. M. Keck Observatory and took more than five hours over a single night. This allowed them to measure how abundant 16 chemical elements are in the star’s atmosphere. They found that carbon, nitrogen, and oxygen were about 10, 8, and 3 percent respectively of that measured in the Sun. By comparison, heavier elements like calcium and iron in the star are approximately one-millionth that of the Sun's.

“This result is very exciting,” said Keck Observatory Chief Scientist John O’Meara. “It tells us about some of the earliest times in the universe by using stars in our cosmic back yard. I look forward to seeing more measurements like this one so we can better understand the earliest seeding of oxygen and other elements throughout the young universe.”

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