A new study suggests that the first water molecules in the universe may have formed far earlier than previously assumed —potentially just 100 to 200 million years after the big bang.
This timeline places the appearance of water well before the formation of galaxies, upending long-standing theories about the earliest conditions that could support life.
How Cosmic Explosions Gave Birth To Water
In the primordial universe, only the lightest elements — primarily hydrogen and helium, with traces of lithium — existed. Oxygen, a key component of water, had yet to appear. The first stars, born out of gravitational clumping of hydrogen gas, changed this. Through nuclear fusion, these early massive stars forged heavier elements in their cores, including oxygen.
When these stars ended their life cycles in supernova explosions, they dispersed these heavier elements into the surrounding space. For the first time, oxygen atoms could bond with abundant hydrogen, forming water molecules.
Simulating The Birth Of Water
The study published in Nature Astronomy, led by the astrophysicist Daniel Whalen and his team at the University of Portsmouth, developed complex computer simulations to model this sequence of events. They recreated the conditions under which the first stars formed and exploded, focusing on two categories: stars 13 times the mass of the Sun, and behemoths up to 200 times its mass.
Their findings revealed that these explosive events could lead to the creation of vast vapor clouds. The smallest stars in the simulations produced enough water to equal Earth’s mass, while the largest generated vapor clouds with the mass of Jupiter.
“To do anything less, you really just don’t know what’s happening,” said Whalen, emphasizing the importance of simulating supernova events in realistic cosmological environments.
Water Before Galaxies
According to the simulations, water formation began as soon as 3 million years after a supernova, with the process sometimes taking up to 90 million years. This means water could have formed as early as 100 million years post-big bang.
Even more striking, the research showed that gravity caused the newly formed water and other heavy elements to clump together. These dense regions became the birthplaces of second-generation stars — and potentially the first planets.
“That was a huge result,” Whalen said, referring to the gravitational clustering of water and heavy elements.
Early Universe, Early Life? The Paradigm Is Shifting
Astronomers have uncovered evidence that water vapor may have existed in the universe far earlier than previously believed—possibly even before the first galaxies formed. The findings suggest that the building blocks for life could have emerged in environments far more ancient and extreme than scientists once imagined.
“This idea that water formed even before galaxies did basically overturns decades of thought about when life could have first emerged in the universe,” explained Whalen.
Muhammad Latif, a team member from United Arab Emirates University, noted that the researchers plan to explore whether early water vapor could have survived the intense radiation during galaxy formation. Their goal is to determine if some of these ancient molecules may still exist — possibly even on Earth.
“The chemistry of life as we know it requires liquid water, and that you can get only on a planet or some object that has a surface with an atmosphere,” said Avi Loeb of Harvard University.
If confirmed, the presence of primordial water vapor could shift not just the timeline of cosmic chemistry—but the very origins of where, and how, life itself might have begun.