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Home SCIENCE What was it like when the first “polluted” stars formed? | by Ethan Siegel | Starts With A Bang! | Jan, 2024

What was it like when the first “polluted” stars formed? | by Ethan Siegel | Starts With A Bang! | Jan, 2024

by California Digital News

When the very first stars form in the Universe, they form out of hydrogen and helium alone. But when that first generation dies, it can give rise to a second generation that’s far more complex, intricate, and diverse. The resulting starburst from the forming of the second generation of stars may resemble Henize 2–10, a nearby star-forming galaxy located 30 million light years away. (Credit: NASA, ESA, Zachary Schutte (XGI), Amy Reines (XGI); Processing: Alyssa Pagan (STScI))

The first stars in the Universe were made of pristine material: hydrogen and helium alone. Once they die, nothing escapes their pollution.

When you look out at the Universe today, and see the vast, dark, backdrop littered with points of light that correspond to stars and galaxies, it’s difficult to imagine that it used to be almost identical everywhere. The Universe, back at its inception, was almost perfectly uniform on all cosmic scales. It was the same high temperature everywhere, the same large density everywhere, and was made up of the same quanta of matter, antimatter, dark matter, and radiation in all locations. At the earliest times, the only differences that existed were minuscule, at the 0.003% level, seeded by the quantum fluctuations imprinted during inflation.

But gravity and time have a way of changing everything. Over time, the excess antimatter annihilates away; first atomic nuclei and then neutral atoms form; over millions of years, gravity pulls matter into overdense regions, causing them to grow. Because overdensities differ by such great amounts on all scales, there are regions where stars form rapidly, within 100 million years or fewer, while other regions won’t begin forming stars for billions of years. But wherever the earliest stars form, that’s where the most interesting things happen first, including the existence of the second generation of stars: the first polluted stars in all of cosmic history.

An illustration of the first stars turning on in the Universe. Without metals to cool down the clumps of gas that lead to the formation of the first stars, only the largest clumps within a large-mass cloud will wind up becoming stars: fewer in number but greater in mass than today’s stars. (Credit: NASA / WMAP Science Team)

The very, very first stars are born in the most initially overdense regions of all, which grow by attracting surrounding matter the fastest. The gravitational growth of matter leads to the first stars forming somewhere between 50 and 100 million years after the Big Bang, with those stars being much more massive than the stars we see today. Because there’s so much mass inside them, undergoing the rapid, high-temperature reactions of nuclear fusion, they live fast. Within just a few million years, they’ve burned through all of their core’s fuel, leading to their dying in either a supernova or by…

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