The first stars in the cosmos may have been more than 10,000 times the mass of Sunabout 1,000 times larger than the largest stars alive today, a new study has found.
Today the largest stars are 100 solar masses. But the early universe it was a much more exotic place, filled with megagiant stars that lived fast and died very, very young, the researchers found.
And once these doomed giants died out, the conditions were never right for them to form again.
Related: Our Expanding Universe: Age, History, and Other Facts
The cosmic dark ages
More than 13 billion years ago, not long after the big Bang, the universe had no stars. There was nothing but a warm soup of neutral gas, made up almost entirely of hydrogen and helium. However, over hundreds of millions of years, that neutral gas began to accumulate into increasingly dense balls of matter. This period is known as the cosmic Dark Ages.
In the modern universe, dense balls of matter rapidly collapse to form stars. But that’s because the modern universe has something the early universe lacked: many elements heavier than hydrogen and helium. These elements are very efficient at radiating energy. This allows dense clumps to shrink very quickly, collapsing to densities high enough to trigger nuclear fusion – the process that powers stars by combining lighter elements into heavier ones.
But the only way to get heavier elements in the first place is through the same process of nuclear fusion. Multiple generations of stars forming, merging, and dying enriched the cosmos to its current state.
Without the ability to quickly release heat, the first generation of stars had to form under very different and much more difficult conditions.
To understand the puzzle of these early stars, a team of astrophysicists turned to sophisticated dark age computer simulations to understand what was happening at the time. They reported their findings in January in an article published in the arXiv preprints database (opens in a new tab) and submitted for peer review to the Monthly Notices of the Royal Astronomical Society.
The new work features all the usual cosmological ingredients: Dark matter to help grow galaxies, the evolution and agglutination of the neutral gas and the radiation that can cool and sometimes reheat the gas. But his work includes something others have lacked: cold fronts, fast-moving streams of cold matter, hitting already formed structures.
The researchers found that a complex web of interactions preceded the first star formation. The neutral gas began to accumulate and clump together. The hydrogen and helium released some heat, allowing the clumps of neutral gas to slowly reach higher densities.
But the high-density clumps got very hot, producing radiation that disintegrated the neutral gas and prevented it from breaking up into many smaller clumps. That means that the stars formed by these clumps can become incredibly large.
These back-and-forth interactions between radiation and neutral gas gave rise to massive reservoirs of neutral gas, the beginnings of the first galaxies. Gas in the depths of these protogalaxies formed rapidly spinning accretion disks: fast-flowing rings of matter that form around massive objects, including black holes in the modern universe.
Meanwhile, at the outer edges of the protogalaxies, cold fronts of gas rained down. The coldest and most massive fronts penetrated the protogalaxies up to the accretion disk.
These cold fronts smashed into the disks, rapidly increasing both their mass and density to a critical threshold, allowing the first stars to appear.
Those early stars weren’t just normal fusion factories. They were giant lumps of neutral gas that ignited their fusion nuclei at once, skipping the stage where they fragmented into small pieces. The resulting stellar mass was enormous.
Those first stars would have been incredibly bright and would have lived extremely short lives, less than a million years. (Stars in the modern universe can live for billions of years.) After that, they would have died in furious bursts of supernova explosions
Those explosions would have carried the products of internal fusion reactions, elements heavier than hydrogen and helium, which then seeded the next round of star formation. But now contaminated by heavier elements, the process could not be repeated, and those monsters would never appear on the cosmic scene again.
Originally posted on LiveScience.com.
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