According to a new study, the early universe was densely packed with stars 10,000 times the size of our sun

 According to a new study, the first stars in the universe may have topped out at over 10,000 times the mass of the sun, making them roughly 1,000 times larger than the largest stars alive today.

The largest stars now have 100 solar masses. The early universe, however, was a far more exotic place, filled with mega-giant stars that lived fast and died young, the researchers discovered.

And once these doomed giants died out, the conditions were never favourable for them to reappear.

The apocalyptic dark ages

The universe had no stars more than 13 billion years ago, not long after the Big Bang. Nothing but a warm soup of neutral gas, almost entirely composed of hydrogen and helium. However, over hundreds of millions of years, that neutral gas began to accumulate into increasingly dense balls of matter. This is referred to as the "cosmic Dark Ages."

Dense balls of matter quickly collapse to form stars in the modern universe. But this is because the modern universe contains many elements heavier than hydrogen and helium, which the early universe lacked. These elements are extremely effective at dissipating energy. This allows the dense clumps to shrink very quickly, eventually collapsing to densities high enough to trigger nuclear fusion—the process that powers stars by combining lighter elements into heavier ones.

However, the only way to obtain heavier elements in the first place is through nuclear fusion. The cosmos has been enriched by multiple generations of stars forming, fusing, and dying.

The first generation of stars had to form under much different and more difficult conditions because they lacked the ability to rapidly release heat.

Fronts of cold weather

A team of astrophysicists used sophisticated computer simulations of the dark ages to understand what was going on back then to solve the puzzle of these first stars. They published their findings in the preprint database arXiv in January and submitted it for peer review to the Monthly Notices of the Royal Astronomical Society.

The new study includes all of the standard cosmological ingredients: dark matter to aid in the formation of galaxies, neutral gas evolution and clumping, and radiation that can cool and sometimes reheat the gas. Their work, however, includes something that others have not: cold fronts, which are fast-moving streams of chilled matter that slam into already-formed structures.

The researchers discovered that the first star formation was preceded by a complex web of interactions. Neutral gas began to clump together and collect. The release of heat by hydrogen and helium allowed clumps of the neutral gas to gradually reach higher densities.

However, high-density clumps became extremely hot, emitting radiation that broke apart the neutral gas and prevented it from fragmenting into many smaller clumps. As a result, stars formed from these clumps can grow enormously large.

Supermassive galaxies

These back-and-forth interactions between radiation and neutral gas resulted in massive pools of neutral gas, which served as the foundation for the first galaxies. The gas deep within these proto-galaxies formed rapidly spinning accretion discs—fast-flowing rings of matter that form around massive objects in the modern universe, including black holes.

Meanwhile, cold fronts of gas rained down on the protogalaxies' peripheries. Cold, massive fronts penetrated proto-galaxies all the way to the accretion disc.

Those first stars were not ordinary fusion reactors. They were massive clumps of neutral gas that ignited their fusion cores all at once, bypassing the stage where they fragmented into small pieces. The resultant stellar mass was enormous.

Those first stars would have been extremely bright and lived for a very short time—less than a million years. (In the modern universe, stars can live for billions of years.) They would have died in ferocious supernova explosions after that.

These explosions would have carried the byproducts of internal fusion reactions—elements heavier than hydrogen and helium—which would have sparked the next round of star formation. But because the process had been tainted by heavier elements, it couldn't be repeated, and those monsters would never appear again on the cosmic stage.

By : LIVESCIENCE