An illustration showing a shimmering burst of starlight at the center of a turbulent field of crackling orange radiation and glowing black holes. (Image credit: ESA)
A new study has found that the first stars in space may have been more than 10,000 times the mass of the Sun, about 1,000 times the mass of the largest living stars.
Currently, the largest stars have a mass of 100 solar masses. But the early universe was a much more exotic place, filled with mega-giant stars that lived fast and died very young, the researchers found.
And once these doomed giants died out, the conditions for their re-formation were never right.
Related: Our Expanding Universe: Age, History and Other Facts
Cosmic dark ages
More than 13 billion years ago, shortly after the Big Bang, there were no stars in the universe. There was nothing but a warm soup of neutral gas, composed almost entirely of hydrogen and helium. However, over hundreds of millions of years, this neutral gas began to accumulate into increasingly dense balls of matter. This period is known as the Space Middle Ages.
In the modern universe, dense balls of matter are rapidly collapsing to form stars. But that’s because the modern universe has something that the early universe lacked: lots of elements heavier than hydrogen and helium. These elements radiate energy very efficiently. This allows dense clusters to collapse very quickly, collapsing to a density high enough to trigger nuclear fusion, the process that powers stars by fusing lighter elements into heavier ones.
But the only way to get heavier elements is through the same process of nuclear fusion. The many generations of stars that formed, merged and died enriched the cosmos to its current state.
Without the ability to quickly release heat, the first generation of stars must have formed in completely different and much more difficult conditions.
Stars form when clouds of dust and gas collapse, causing nuclear fusion inside dense balls of material. (Image credit: NASA/ESA/Hubble Heritage Team (STScI/AURA))
cold fronts
To understand the mystery of these first stars, a group of astrophysicists turned to sophisticated computer simulations of the dark ages to understand what was happening then. They reported their findings in January in an article published in the arXiv preprint database. (will open in a new tab) and submitted for review in the Monthly Notices of the Royal Astronomical Society.
The new work presents all the usual cosmological ingredients: dark matter that helps galaxies grow, the evolution and condensation of neutral gas, and radiation that can cool and sometimes heat gas. But their work has something that others have lacked: cold fronts – fast-moving streams of chilled matter – that crash into already formed structures.
The researchers found that the first star formation was preceded by a complex network of interactions. Neutral gas began to collect and stick together. The hydrogen and helium gave off some heat, which allowed the neutral gas clumps to slowly reach higher densities.
But the high-density clumps became very warm, producing radiation that decomposed the neutral gas and prevented it from disintegrating into many smaller clumps. This means that stars made up of these clumps can become incredibly large.
This artist’s impression shows a heat wave burst detected in a massive star being formed. (Image credit: Katharina Immer/JIVE)
supermassive stars
These reciprocating interactions between radiation and neutral gas led to massive accumulations of neutral gas, the beginning of the first galaxies. Gas deep within 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, cold gas fronts hit the outer edges of the protogalaxies. The coldest, most massive fronts penetrated protogalaxies up to the accretion disk.
These cold fronts crashed into the disks, rapidly increasing their mass and density to a critical threshold, thus allowing the first stars to emerge.
Those first stars were not just ordinary fusion factories. They were giant clumps of neutral gas that simultaneously ignited all their thermonuclear nuclei, skipping the stage at which they decay into small pieces. The resulting stellar mass was enormous.
These first stars would have been incredibly bright and would have had 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 flashes of supernova explosions.
These explosions were supposed to carry the products of internal fusion reactions – elements heavier than hydrogen and helium – which then laid the foundation for the next round of star formation. But now, infested with heavier elements, the process could not be repeated, and these monsters never appeared again on the cosmic scene.
Originally published on LiveScience.com.
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