Ancient star sheds new light on the birth of the universe

Astronomers have discovered an extremely old star on the edge of our galaxy that appears to have only formed a few million years after the Big Bang – and what they learn from it could affect their understanding of the birth of the universe.

In a study published last week, the researchers discovered the star during an astronomical study of the southern sky with a technique called narrowband photometry, which measures the brightness of distant stars in different wavelengths of light and can reveal stars that have low levels of heavy elements.

They then studied the star – known by its survey number as SPLUS J210428.01−004934.2, or SPLUS J2104−0049 for short – with high-resolution spectroscopy to determine its chemical composition.

They have now determined that it is one of the very few “ultra poor metal” stars, or UMPs, which means it is one of the oldest stars ever to be seen.

“They are very rare – we only know of 35 after searching for decades,” said astronomer Vinicius Placco of the National Science Foundation’s Astronomical Research Laboratory NOIRLab in Tucson, Arizona.

He said that SPLUS J2104−0049 – a red giant star with about 80% of the sun’s mass – is at least 10 billion years old and maybe just a few million years younger than the universe itself. , that astronomers estimate is 13.8 billion years.

Placco is the lead author of the study published in Astrophysical Journal Letters on the distant star.

The researchers used data from an astronomical telescope survey at Cerro Tololo in northern Chile. He revealed the star in our galaxy’s halo, far beyond the Milky Way’s main disk and about 16,000 light years from Earth – far too far away to be seen with the naked eye.

Placco said the original survey covered around 20 million stars, of which he selected around 200 to study by medium-resolution spectroscopy using NOIRLab’s Gemini South telescope, a few kilometers from Cerro Pachon in the Chilean Andes. .

SPLUS J2104−0049 was found to be of particular interest and was therefore studied in more detail with high resolution spectroscopy using US-operated Magellan telescopes in the Atacama Desert in Chile, about 100 miles further north, did he declare.

Observations show that SPLUS J2104−0049 is extremely poor in heavy elements and has one of the lowest carbon levels recorded. This implies that this is a very first “Population II” star that formed from the remnants of exploded “Population III” stars – the very first population of pristine stars, containing only hydrogen and helium, which formed only a few million years after matter was created in the Big Bang.

So far, no one has found a Population III star. The larger the mass of a star, the faster it burns, and it is believed that most of the stars in Population III were extremely large and burned out a long time ago.

Most stars, like the sun, are third generation “population I” stars that contain relatively heavy elements such as iron, nickel, carbon, and oxygen. These heavy elements were created by fusion within population II stars which exploded into supernovas and seeded them in interstellar clouds.

It is estimated that our sun, which contains about 2% of its mass as heavier elements, is 4.6 billion years. Astronomers believe he still has 5 billion years ahead of him swells into a giant red star which will engulf the Earth and then shrink into a white dwarf star.

Placco said modeling the conditions under which SPLUS J2104−0049 formed suggests that it merged from an interstellar cloud polluted by the supernova of a single population III star with about 30 times the mass of our sun.

The models also suggest that the star Population III it formed from had a different fusion process than expected, which could lead to a better understanding of interstellar conditions in the early universe.

The discovery shows the value of narrowband photometry surveys in identifying stars that are ultra-poor in metals and suggests that even more could be found, he said.

It is even possible that research in this way could lead to the discovery of a true Population III star that formed soon after the Big Bang, although it would need to have the mass of the sun or more. small for surviving so long without burning all of its fuel, Placco says.

Astronomer Howard Bond of Pennsylvania State University said the new method was the development of an early technique for identifying stars poor in metals.

The Star of Methuselah is the oldest known star in our galaxy.NASA

Bond conducted studies on the oldest known star in Population II – nicknamed HD 140283, or “Methuselah Star”, after an extremely long patriarch in the Bible – who is about 200 light years from Earth and estimated to be over 13.5 billion years old.

He noted that while a star’s composition can be determined spectroscopically, determining a star’s age requires knowing its distance from Earth with very high precision.

SPLUS J2104−0049 was presumably very old, and might even be older than HD 140283, but “it will be very difficult to really determine its age because it is at a relatively large distance,” he said.

Meanwhile, the search for the original Population III stars continues: “No one has found a truly virgin star made only of hydrogen and helium,” he said.

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