The early universe, fresh from the Big Bang, was a hot, dense soup of simple elements: hydrogen, helium, and trace amounts of lithium. But within a cosmic blink—just 100 to 200 million years after the birth of the universe—water began to form. That’s according to a new study, which found that one of the essential ingredients for life existed far earlier than scientists ever imagined.
It’s perhaps poetic that the first fire-quenching water was formed by cosmic explosions in primordial infernoes. When some of the first stars, known as Population III stars, died, they didn’t fade quietly. These giant stars, some hundreds of times more massive than our sun, exploded in supernovae events, seeding the cosmos with heavy elements — but also oxygen. It didn’t take long for oxygen to combine with hydrogen to form what would one day become oceans and even life itself.
“Before the first stars exploded, there was no water in the Universe because there was no oxygen,” said Daniel Whalen, a cosmologist at the University of Portsmouth and lead author of the study. “Only very simple nuclei survived the Big Bang—hydrogen, helium, lithium, and trace amounts of barium and boron.”
The Birth of Water in a Violent Universe
Using sophisticated computer simulations, a team of astrophysicists modeled the explosions of two types of primordial stars: a 13-solar-mass star and a behemoth 200-solar-mass star. These stars, born just 100 to 200 million years after the Big Bang, lived fast and died young, exploding as supernovae that scattered their elements across the cosmos.
The simulations showed that as these supernovae expanded and cooled, oxygen from the explosions reacted with hydrogen to form water. Both types of explosions produced dense clumps of gas enriched with water as a result of the supernova debris.
The primary sites of water production in primordial supernovae are dense, self-gravitating cores in the ejecta. These cores, rich in water and dust, are also the likely birthplaces of the first protoplanetary disks—the swirling clouds of gas and dust that give rise to new stars and planets.
“Although the total water masses were modest, they were highly concentrated in the only structures capable of forming stars and planets. And that suggests that planetary discs rich in water could form at cosmic dawn, before even the first galaxies,” Whalen said.
Water formed in staggering amounts and almost in the blink of an eye in relative cosmic time. Within just 3 million years of the collapse of the largest Population III stars, the surrounding gas contained a thousand times more water than the amount produced by a smaller supernova. Some of this water would have been destroyed by the intense radiation from young, massive stars, but rising levels of dust in early galaxies may have shielded it, allowing it to survive.
If water existed in the universe just 100 to 200 million years after the Big Bang, the conditions necessary for life may have been in place far earlier than scientists ever imagined. The long-held view has always been that water—and the potential for life—emerged much later in the universe’s history.
The next step is to look for evidence of this primordial water in the real universe. The researchers suggest that future telescopes, like the Square Kilometer Array and the Next Generation Very Large Array, might be able to detect the faint signals of water masers—intense beams of microwave radiation emitted by water molecules—from these ancient galaxies.
The findings appeared in the journal Nature Astronomy.
