The Large Magellanic Cloud (LMC) is the Milky Way\u2019s most massive satellite galaxy. Because it\u2019s so easily observed, astronomers have studied it intently. They\u2019re interested in how star formation in the LMC might have been different than in the Milky Way.<\/p>\n
A team of researchers zeroed in on the LMC\u2019s most metal-deficient stars to find out how different. <\/p>\n
<\/p>\n The LMC is about 163,000 light-years away and about 32,000 light-years across. Even though it\u2019s that large, it\u2019s still only 1\/100th the mass of the Milky Way. It was probably a dwarf spiral galaxy before gravitational interactions with the Milky Way and the Small Magellanic Cloud warped its shape. Scientists predict it\u2019ll probably merge with the Milky Way in about 2.4 billion years. <\/p>\n The LMC wasn\u2019t always this close to the Milky Way. It formed elsewhere in the Universe, out of a different reservoir of gas than the Milky Way. The LMC\u2019s stars preserve the environmental conditions they formed in. <\/p>\n The first stars to form in the Universe were the most metal-poor stars. When they formed, only hydrogen and helium from the Big Bang were available. These stars are called Population 3 stars, and they\u2019re largely hypothetical. They were massive and many of them exploded as supernovae. These stars forged the heavier elements, called metals in astronomy, and then spread them out into space to be taken up by the next stars to form. That process continued generation by generation. <\/p>\n Nobody\u2019s ever found a Population 3 star because even if they\u2019re more than hypothetical, they\u2019d all be long gone by now. But in new research, scientists examined 10 of the LMC\u2019s most metal-poor stars. They found one Population 2 star that is so metal-poor it\u2019s similar to Population 3 stars. <\/p>\n The research is titled \u201cEnrichment by extragalactic first stars in the Large Magellanic Cloud.\u201d It\u2019s published in the journal Nature Astronomy. The lead author is Anirudh Chiti from the Department of Astronomy & Astrophysics and the Kavli Institute for Cosmological Physics, both at the University of Chicago.<\/p>\n \u201cThis star provides a unique window into the very early element-forming process in galaxies other than our own,\u201d said lead author Chiti. \u201cWe have built up an idea of how these stars that were chemically enriched by the first stars look like in the Milky Way, but we don\u2019t yet know if some of these signatures are unique or if things happened similarly across other galaxies.\u201d<\/p>\n The earliest Population 3 stars changed the Universe. By producing metals, they guaranteed the stars to follow had higher metallicities. But exactly what metals did they produce, and how much?<\/p>\n \u201cWe want to understand what the properties of those first stars were and what were the elements they produced,\u201d said Chiti.<\/p>\n The difficult part is that nobody\u2019s ever seen a Population 3 star. But by identifying an extremely metal-poor star that\u2019s very similar to the first stars, the researchers found the next best thing. Finding nine other metal-poor stars was also helpful.<\/p>\n They compared the 10 LMC metal-poor stars to metal-poor stars in the Milky Way. The results show how different processes and different environments in both galaxies affected star formation and metal enrichment. <\/p>\n These metal-poor stars are difficult to find. Most of the stars in the Universe resulted from successive generations of stars; their enriched metallicity is a testament to that. Our Sun is a metal-rich Population 1 star, for example. <\/p>\n But these older, metal-poor Population 2 stars are out there. Since astronomers will likely never find an ancient Population 3 star, the Population 2 stars with the lowest metallicities are the next best things.<\/p>\n \u201cMaybe fewer than 1 in 100,000 stars in the Milky Way is one of these second-gen stars,\u201d Chiti said. \u201cYou really are fishing needles out of haystacks.\u201d<\/p>\n But once astronomers find them, the outer layers of these rare stars hold evidence of the conditions they formed in. \u201cIn their outer layers, these stars preserve the elements near where they formed,\u201d Chiti explained. \u201cIf you can find a very old star and get its chemical composition, you can understand what the chemical composition of the universe was like where that star formed billions of years ago.\u201d<\/p>\n Finding such metal-poor stars in the LMC allowed astronomers to compare the star-forming conditions in that satellite galaxy to those in the Milky Way. The comparison can help astrophysicists understand how these star-forming conditions may have differed. <\/p>\n One of the 10 stars in the LMC stood out from the rest. It had markedly lower metallicity than the other nine. Called LMC 119, it\u2019s 50 times more metal-deficient than the others. \u201cGiven its extremely low metallicity, this star exhibits the characteristics of a second-generation star that preserves the chemical imprints of a first-star supernova,\u201d the authors write.<\/p>\n One fact stood out to the researchers when they mapped LMC 119\u2019s elements. It had much less carbon than iron when compared to Milky Way stars. In fact, the same was true of all 10 stars in the sample. This is important because the LMC wasn\u2019t always a satellite galaxy of the Milky Way. That association only goes back a couple of billion years or so. Its stars formed in a distant region of the high-redshift Universe. <\/p>\n \u201cThat was very intriguing, and it suggests that perhaps carbon enhancement of the earliest generation, as we see in the Milky Way, was not universal,\u201d Chiti said. \u201cWe\u2019ll have to do further studies, but it suggests there are differences from place to place.\u201d<\/p>\n For Chiti and his colleagues, the conclusion is clear. \u201cThis, and other abundance differences, affirm that the extragalactic early LMC experienced diverging enrichment processes compared to the early Milky Way. Early element production, driven by the earliest stars, thus appears to proceed in an environment-dependent manner,\u201d they write in their conclusion.<\/p>\n Since Chiti and his fellow researchers found one very low-metallicity star in the LMC, there are probably many more among its suspected population of 20 billion stars. Chiti is leading a program to map out more stars in the southern sky and find more of these types of stars. <\/p>\n \u201cThis discovery suggests there should be many of these stars in the Large Magellanic Cloud if we look closely,\u201d he said. \u201cIt\u2019s really exciting to be opening up stellar archeology of the Large Magellanic Cloud and to be able to map out in such detail how the first stars chemically enriched the universe in different regions.\u201d <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2023\/01\/STScI-01EVT45HQKNHQRSF0EYER8XWF3.jpg\")
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