Astronomers discover what could be one of the oldest stars in the known universe

A red giant star 16,000 light years away appears to be a bona fide member of the second generation of stars in the Universe.

Based on an analysis of its chemical abundances, it appears to contain elements produced in the life and death of a single first-generation star. Therefore, with its help, we might even find the first generation of ever-born stars – none of which have yet been discovered.

Additionally, the researchers performed their analysis using photometry, a technique that measures the intensity of light, providing a new way to find these ancient objects.

“We report the discovery of SPLUS J210428.01−004934.2 (hereinafter SPLUS J2104−0049), an ultra-poor metal star selected from its narrowband S-PLUS photometry and confirmed by medium and high resolution spectroscopy , ” the researchers wrote in their article.

“These proof of concept observations are part of an ongoing effort to spectroscopically confirm low metallicity candidates identified from narrowband photometry.”

While we feel like we have a pretty good grasp of how the Universe went from the Big Bang to the starry glory we know and love today, the first stars to turn on their flashing lights in the Primordial Darkness, known as Population III stars, remain something of a mystery.

Current star-forming processes give us clues as to how these early stars came together, but until we find them, we base our understanding on incomplete information.

The stars of Population II are a trail of breadcrumbs – the next generations following Population III. Of these, the generation immediately succeeding Population III is perhaps the most exciting, as it is the closest in composition to Population III.

We can identify them by their very low abundance of elements like carbon, iron, oxygen, magnesium and lithium, detected by analyzing the spectrum of light emitted by the star, which contains the chemical fingerprints of the elements. that are there.

Indeed, before the creation of the stars, there were no heavy elements – the Universe was a kind of cloudy soup composed mainly of hydrogen and helium. When the first stars formed, that is also what they should have been made of – it was through the process of thermonuclear fusion in their nucleus that the heaviest elements were formed.

First, hydrogen is fused into helium, then helium into carbon, and so on down to iron, depending on the mass of the star (the smaller ones do not have enough energy to fuse helium into carbon and end their life (when they reach that point). Even the most massive stars do not have enough energy to fuse iron; when their core is completely iron, they become supernovae.

These colossal cosmic explosions spit out all this molten matter in near space; moreover, the explosions are so energetic that they generate a series of nuclear reactions which forge even heavier elements, such as gold, silver, thorium and uranium. Baby stars then forming from clouds containing these materials have a higher metallicity than previous stars.

Today’s stars – Population I – have the highest metallicity. (By the way, this means that ultimately no new star will be able to form, because the The universe’s hydrogen supply is limited – good times.) And stars that were born when the Universe was very young have very low metallicity, the first stars being called ultra-poor metal stars or UMP stars.

These PMUs are considered bona fide Population II stars, enriched with material from a single Population III supernova.

Using a photometric survey called S-PLUS, a team of astronomers led by the National Science Foundation’s NOIRLab identified SPLUS J210428-004934, and although it does not yet have the lowest metallicity that we detected (this honor belongs to SMSS J0313-6708), it has an average metallicity for a UMP star.

It also has the lowest abundance of carbon astronomers have ever seen in an ultra-low metal star. This could give us an important new constraint on progenitor star and stellar evolution models for very low metallities, the researchers said.

To understand how the star could have formed, they performed theoretical modeling. They found that the chemical abundances observed in SPLUS J210428-004934, including the abundances of low-carbon stars and more normal UMPs of other elements, could be better reproduced by a high-energy single-star supernova. Population III 29.5 times the mass of the Sun. .

However, the fits closest to modeling were still unable to produce enough silicon to exactly replicate SPLUS J210428-004934. They recommended looking for older stars with similar chemical properties to try and resolve this strange discrepancy.

“Additional UMP stars identified from S-PLUS photometry will dramatically improve our understanding of Pop III stars and help find a low-mass, metal-free star still living in our galaxy today.” the researchers wrote.

Their article was published in Letters from the astrophysical journal.