Water is an essential part of life on Earth, and possibly elsewhere – and now it we know it may have formed not long after the start of the universe
By Sophie Berdugo
4 March 2025
Water was born as the result of exploding stars
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The first water molecules may have formed just 100 million to 200 million years after the big bang – before even the first galaxies – kicking off a process that led to life on Earth… and possibly elsewhere.
Shortly after the big bang, most of the matter in the universe was hydrogen and helium, with only trace amounts of other lighter elements, like lithium. Heavier elements like oxygen didn’t yet exist, making it impossible for water to form.
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Those initial elements came together in the first stars, which then produced heavier elements through nuclear fusion including, crucially, oxygen. When these stars reached the end of their lives, they exploded as supernovae, releasing these heavier elements and allowing oxygen to mix and combine with the pre-existing hydrogen to create H2O – water.
Previous research has shown that even the relatively low amounts of oxygen produced in the earliest stars could have made water molecules, but until now nobody had simulated exactly what would happen when a primordial star went supernova and and how the elements it released would mix with the cosmological environment in which the star formed, says Daniel Whalen at the University of Portsmouth in the UK. “To do anything less, you really just don’t know what’s happening,” he says.
To investigate this, Whalen and his team used computer models to simulate the birth and death of the first stars in a realistic context. These early stars are thought to have ranged from 13 times as massive as the sun to 200 times as massive, so the researchers modelled both extremes.