Water in the universe may have formed closer to the Big Bang than previously thought

When did life as we know it first emerge in the universe?

We don’t know for sure, but the answer is inextricably linked to the moment when water first materialized in the cosmos — and new simulations suggest the very first generation of stars helped form such life-giving water just 100 million to 200 million years after the Big Bang. This pushes back previous estimates by more than 500 million years.

"We were surprised that water could actually form so early on — even before the birth of the first galaxies," study co-author Muhammad Latif of the United Arab Emirates University told Space.com. The findings suggest that if some of this initial reservoir of water survived the heat-filled chaos of early galaxy formation, it could have been absorbed into newborn planets, potentially leading to habitable, water-rich worlds just a couple hundred million years after the Big Bang. "It's all connected with the story of how early life can start in the universe," Latif said.

Previous observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile suggested that water existed about 780 million years after the Big Bang, when the young universe was chock-full of lightweight hydrogen and helium along with small amounts of lithium. These elements formed the first generation of stars, known to astronomers as Population III stars, which were enormous — up to dozens or even hundreds of times the mass of our sun — and lived notably short lives before dying as supernovas. Many of the universe's heavier elements, including oxygen, were forged within these stars through nuclear reactions and dispensed into space upon their deaths, where they were later incorporated into the next generation of stars.

To determine when water first formed in the universe, Latif and his colleagues used numerical models to trace the life cycles of two first-generation stars: one was 13 times heavier than our sun, and the other was 200 times heavier than our star. The smaller virtual star lived for 12.2 million years before dying in an explosive supernova, dumping about 0.051 solar masses of oxygen (nearly 17,000 Earth masses) into its surrounding space. The larger simulated star burned through its fuel in just 2.6 million years before meeting its own explosive end, showering a whopping 55 solar masses of oxygen (more than 18 million Earth masses) into space.

The simulations revealed that as shockwaves from each supernova radiated outward, turbulent density fluctuations created ripples that led some of the gas to coalesce into dense clumps. These leftover clumps, enriched by metals including oxygen ejected by supernovas, were likely the primary sites for water to form across the early universe.

Nestled within denser parts of the clouds, the water would have been protected from being destroyed by harsh radiation from nearby stars, Latif said. However, his team considered the simplest case of just one star forming in each clump, whereas theoretical simulations suggest multiple star systems to be the norm; more than half of all stars in the sky have one or more siblings. Multiple nearby stars would mean more dense, water-enriched clumps, but also a lot more radiation, which "might change a few things, but we still expect water might to survive," said Latif. "These are the first questions that we tried to answer, but we need more people to be working on this topic and explore this in more detail."

Follow-up simulations by his team suggest these water-harboring clumps are also favorable sites for habitable worlds to coalesce. Whether water within these clumps could have persisted through billions of years of cosmic evolution, and if so, how, is not yet fully understood. One leading theory suggests comets may have delivered water to Earth, but any such icy transporters from the early universe are not expected to have survived the harsh conditions of the Epoch of Reionization, said Latif, referring to a period about 400,000 years after the Big Bang when ionizing ultraviolet light from the first stars and galaxies pervaded the universe and lifted the primordial cosmic fog. However, the researchers are not yet ruling out the possibility that at least some of the water on Earth may be primordial in origin.

Populations of water-rich planets in the early universe would create faint emissions, Latif said, which could potentially be detected in the coming decade by ALMA or the forthcoming Square Kilometer Array in Australia and South Africa. If such emissions are indeed observed, it would be a "game changer," he said, in that it would shift the paradigm of origin of life to within just a couple hundred million years after the Big Bang.

"It opens a whole new line of research."

The study was published on Monday (March 3) in the journal Nature Astronomy.