April 13, 2024

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They found, next to the Milky Way, one of the oldest stars in the universe

They found, next to the Milky Way, one of the oldest stars in the universe

There was a time when hydrogen and helium were the only materials available in the universe for star formation. Only later, after the first stellar generation began to fuse other elements within itself and “seed” space with them after its death, were the stars of subsequent generations able to fuse them and, eventually, allow planets like ours to form.

The “metallicity” of a star, i.e. the presence of elements other than the original hydrogen and helium in it, is actually one of the most important indicators for determining its age. The low metallicity in the star's formation means it was born early in the universe's history, when there were far fewer elements at its disposal.

For astronomers, the “holy grail” would be stars devoid of any metallicity, i.e. first-generation stars. But no one has yet been able to find one. Scientists believe this is because most of those early stars were so large that they burned up and died very quickly.

second generation

Now, however, a team of researchers led by Anirudh Chetty, of the University of Chicago, has just announced…Nature astronomy“The discovery of a star that, without becoming a member of the first stellar generation, undoubtedly belongs to the second generation.” In fact, it's one of the oldest stars yet observed, and it turns out it's located right next to our galaxy. The star, called LMC 119, is located just 160,000 light-years away, in the Large Magellanic Cloud, our own galaxy. It is the first second-generation star in the universe to be found in another galaxy.

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“This star provides a unique window into the early process of element formation in galaxies other than our own,” explains Chetty. “So far we've got an idea of ​​what these chemically enriched stars looked like from the first stars in the Milky Way, but we still don't know whether some of these signatures are unique or whether the same thing has happened in other galaxies.”

Here, in the Milky Way, many “second generation” stars have already been found, that is, with such low metallicity that they were forcibly formed from the material left over after the first generation exploded and spread throughout the galaxy. . However, these stars are extremely rare (barely one in 100,000), and researchers search for them diligently because finding a star outside the Milky Way can tell us whether or not the materials available to make stars in the early universe were the same. Everywhere. Thanks to Chetty and his team, we now have an example very close to us to answer this question.

Different configuration

“In their outer layers – says Chetty – these stars preserve elements that were close to where they formed. “If you can find a very old star and get its chemical composition, you can understand the chemical composition of the universe in the place where that star was born, billions of years ago.”

Researchers at LMC 119 have found one of the answers they were looking for. In fact, the star's composition turns out to contain much less carbon and iron than that found here, which is very different from second-generation stars in the Milky Way.

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As Chetty put it: “This is very interesting and suggests that the first generation carbon enhancement, as we see in the Milky Way, was not universal. We will have to do more studies, but this suggests that there are differences from place to place.” I think “We complete the picture of what the initial process of enrichment of elements in different environments looked like.”

Researchers believe there may be more of these ancient stars lurking in the Large Magellanic Cloud. Finding them could provide new clues about the childhood of the universe and the differences in the evolutionary paths followed by stars in their different birthplaces.