Shulou(Shulou.com)11/24 Report--

A new study has found that the first stars born in the early universe were tens of thousands of times more massive than the sun, and some stars were even 100,000 times more massive than the sun, equivalent to 1000 of the largest stars in the universe today.

The largest star in the universe today is 100 times the mass of the sun. But researchers found that the early universe was teeming with supermassive stars, all tens of thousands of times the mass of the sun. They are born quickly and have a short life span. And when these giant stars die, the conditions conducive to their re-formation no longer exist.

Shortly after the Big Bang, more than 13 billion years ago, the universe was starless and mostly a hot soup of warm neutral gases, mostly hydrogen and helium. Over hundreds of millions of years, these neutral gases began to pile up into increasingly dense clumps of matter. This period is known as the cosmic dark age.

In the modern universe, dense matter collapses rapidly to form stars. This is because the modern universe has heavy elements that were lacking in the early universe. Heavy elements can radiate energy efficiently, causing dense clumps to contract rapidly, triggering fusion reactions that fuse lighter elements into heavier elements, which are also the source of energy for stars.

But the only way heavy elements can be made in the universe is through the same fusion process. Generations of stars formed, coalesced and died, enriching the universe to its present state.

Because elements such as hydrogen and helium do not have the ability to release heat quickly, the first generation of stars had to form under completely different and very difficult conditions.

To unravel the mystery of how the first stars formed, astrophysicists turned to computer simulations of the evolution of the dark ages of the universe in order to understand what happened. Some early simulations predicted that the first stars might have been hundreds of times the mass of the Sun, while later simulations suggested that they should be the size of normal stars today.

But recently astrophysicists have shown through simulations that stars formed in the early universe were much larger than they are today. In January, they reported their findings in a paper published in the preprint database arXiv and submitted to the Monthly Bulletin of the Royal Astronomical Society for peer review.

The computer simulations in the new study include all the usual cosmological ingredients: dark matter that helps galaxies grow, the evolution and accumulation of neutral gases, and radiation processes that both cool and sometimes reheat gases. But their study also introduces a stream of fast-moving, cooling matter in the universe, a so-called cold front missing from other studies that slams into already formed celestial structures.

The researchers found that before the first stars formed, there was a complex interaction: neutral gases began to clump together; hydrogen and helium gave off a small amount of heat, which slowly increased the density of the neutral gas clump.

But dense clumps of gas become so hot that the radiation produced breaks down the neutral gas and prevents it from breaking up into many smaller clumps. This means that stars formed from these clumps of gas can become very large.

This back-and-forth interaction between radiation and neutral gas gave rise to large amounts of neutral gas, and the first galaxies in the universe were formed in this way. The gas in the depths of protogalaxies first forms a rapidly spinning accretion disk, a ring of rapidly flowing matter around massive objects, including black holes in the modern universe.

At the outer edge of the protogalaxy, cold fronts of gas rain down. The coldest dense streams of matter can penetrate even the protogalaxy and extend all the way to the accretion disk.

These cold fronts slammed into the accretion disks, rapidly increasing their mass and density to critical thresholds, destabilizing the clumps of gas and triggering the instantaneous collapse of large amounts of material that gave birth to the first stars.

The first stars didn't undergo the fusion process typical of the Sun today. They are huge clumps of neutral gas, and the fusion core is triggered directly, skipping the stage where the neutral gas clumps break up into small pieces, making the stars that collapse directly very massive.

The first stars are very bright and short-lived, often less than a million years, before a supernova explodes. Stars in the modern universe, by contrast, can live for billions of years.

The explosion of the first stars hurls the products of internal fusion reactions-elements heavier than hydrogen and helium-into space, planting the seeds for the formation of the next stars.

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