A Johns Hopkins scientist discovers an elusive star with origins close to the Big Bang

Astronomers have discovered what could be one of the oldest stars in the universe, a body almost entirely made up of material spewed by the Big Bang.

The discovery of this tiny star dating back about 13.5 billion years means that more stars with a very low mass and a very low metal content are probably present, perhaps even the very first stars in the universe . The star is unusual because unlike other stars with very low metal content, it is part of the "thin disk" of the Milky Way – the part of the galaxy in which the sun resides. And as this star is so old, researchers say it's possible that our galactic quarter is at least 3 billion years older than expected. The results are about to be published in The astrophysical journal.

"This star is perhaps one in 10 million," said lead author Kevin Schlaufman, an assistant professor in the faculty of physics and astronomy at Johns Hopkins University. "It tells us something very important about the first generations of stars."

The first stars of the universe after the Big Bang would have consisted entirely of elements such as hydrogen, helium and small amounts of lithium. These stars produced heavier elements than helium in their nuclei and sowed the universe when they exploded as supernovae.

The next generation of stars formed from clouds of materials related to these metals, incorporating them into their composition. The metal content, or metallicity, of the stars of the universe increased along with the cycle of birth and death of the stars.

The very weak metallicity of this star indicates that in a cosmic genealogical tree, it could only act from a generation removed from the Big Bang. Indeed, it is the new star record holder with the smallest addition of heavy elements – it has about the same content in heavy elements as the Mercury planet. On the other hand, our sun counts thousands of generations on this line and has a content of heavy elements equal to 14 Jupiters.

Astronomers have found thirty or so old stars, "ultra-poor in metals," with an approximate mass of the sun. Star Schlaufman and her team discovered that their solar mass was only 14%.

The star is part of a two-star system gravitating around a common point. The team discovered the tiny, almost invisible, "secondary" star after another group of astronomers discovered the much brighter "primary" star and measured its composition by studying a high resolution optical spectrum of its light. The presence or absence of black lines in the spectrum of a star makes it possible to identify the elements it contains, such as carbon, oxygen, hydrogen, iron, etc. In this case, the star had a very weak metallicity. These astronomers have also identified unusual behavior in the star system involving the presence of a neutron star or a black hole. Schlaufman and his team felt that it was inaccurate, but so they discovered the much smaller companion of the visible star.

The existence of the smallest companion star turned out to be the great discovery. Schlaufman's team was able to deduce from its mass by studying the slight "wobbling" of the main star as the gravity of the small star pulled it.

By the late 1990s, researchers thought that only large stars could have formed in the earliest stages of the universe. They could never be observed because they burn their fuel and die so quickly.

But as astronomical simulations became more sophisticated, they began to suggest that, in some situations, a star of that time with a particularly small mass could still exist, even more than 13 billion years since the Big Bang. Unlike big stars, the smaller masses can live very long. Red dwarf stars, for example, with a fraction of the mass of the sun, would live billions of years.

The discovery of this new ultra-poor metal star, named 2MASS J18082002-5104378 B, offers the opportunity to observe even older stars.

"If our inference is correct, low-mass stars whose composition is exclusively from the Big Bang may exist," said Schlaufman, also affiliated with the Institute for Data Intensive Engineering and Science. "Even though we have not yet found an object like this in our galaxy, it may exist."

This research is based on observations made with the Magellan Clay Telescope, the Las Campanas Observatory and the Gemini Observatory.