They find, right 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 to make stars. Only later, after that 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 incorporate them and, eventually, allow the formation of planets like the our.

The ‘metallicity’ of a star, that is, the presence in it of elements other than the original hydrogen and helium, is, in fact, one of the most valuable indicators to determine its age. Lower metallicity in a star’s composition means that it was born earlier in the history of the Universe, when there were far fewer elements at its disposal.

For astronomers, the ‘Holy Grail’ would be stars without any metallicity, that is, those of the first generation. But no one so far has managed to find one. Scientists believe this is because most of those early stars were so large that they burned up and died extremely quickly.

The second generation

Now, however, a team of researchers led by Anirudh Chiti, from the University of Chicago, has just announced in ‘Nature Astronomy’ the discovery of a star that, without being a member of the first stellar generation, undoubtedly belongs to the second. In fact, it is one of the oldest stars observed so far, and it turns out to be right next to our own galaxy. Named LMC 119, the star is ‘only’ 160,000 light years away, in the Large Magellanic Cloud, a satellite galaxy of our own. And it is the first second generation star in the Universe to be found in another galaxy.

“This star offers a unique window into the early process of element formation in galaxies other than our own,” explains Chiti. “So far we have gotten an idea of ​​what these stars chemically enriched by the first stars look like in the Milky Way, but we still don’t know if some of these signatures are unique or if the same thing happened in other galaxies.”

Here, in the Milky Way, several ‘second generation’ stars had already been found, that is, with such low metallicity that they must have been formed by force from the material left after the first generation exploded and spread it throughout the galaxy. space. Even so, these are extremely rare stars (barely one in 100,000), and researchers are looking for them diligently since finding one outside the Milky Way can tell us whether the materials available to make stars in the early Universe were, or not, the same everywhere. Thanks to Chiti and his team, we now have an example very close to us to answer that question.

Different composition

«In their outer layers – says Chiti – these stars preserve the elements that were near the place where they were formed. “If you can find a very old star and obtain its chemical composition, you can understand what the chemical composition of the Universe was like in the place where that star was born, billions of years ago.”

The researchers found in LMC 119 one of the answers they were looking for. The composition of the star, in fact, with much less carbon and iron than ‘the ones here’, has turned out to be very different from the second generation stars of the Milky Way.

In Chiti’s words, “This is very intriguing and suggests that perhaps 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 are completing the picture of what the initial process of enriching elements in different environments was like.”

Researchers believe there could be more of these ancient stars lurking in the Large Magellanic Cloud. Finding them could provide new clues about the infancy of the Universe and the differences in the evolutionary paths followed by stars in their different places of birth.

 
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