Water, the essential compound for life on Earth, might have formed far earlier in the universe than previously assumed. New research suggests that water may have been present just 100 to 200 million years after the Big Bang. This discovery challenges earlier expectations and opens up intriguing possibilities about the role of water in the early cosmos and the formation of the first galaxies. Published in Nature Astronomy, the study by Daniel Whalen and his colleagues examines the formation of water in the universe using advanced computer modeling techniques, shedding light on how this life-sustaining molecule could have emerged in the early stages of the universe.
The idea that water might have formed so early has profound implications for our understanding of both cosmic evolution and the conditions necessary for life. Water, as a compound, is made up of hydrogen and oxygen—two elements that, while fundamental to life as we know it, have distinct origins. Hydrogen, the lightest element, and helium, the second lightest, were primarily formed during the Big Bang, while oxygen, a heavier element, forms through nuclear reactions within stars or in explosive supernova events. The question of when and how these elements combined to form water in the early universe has been a subject of much debate.
Whalen and his team sought to answer this question by running computer simulations of two supernovae. These simulations modeled the explosion of two different types of massive stars: one with 13 times the mass of the Sun, and the other with 200 times the mass of the Sun. Supernovae are violent stellar explosions that release enormous amounts of energy and heavy elements into the surrounding space. By analyzing the products of these explosions, the researchers were able to estimate the amount of oxygen that was produced and how it interacted with hydrogen to form water.
The findings were remarkable. In their first simulation, which involved the explosion of a star 13 times the mass of the Sun, the researchers found that the supernova produced about 0.051 solar masses (where one solar mass is the mass of our Sun) of oxygen. In the second simulation, the larger star (200 times the mass of the Sun) produced a far greater quantity—around 55 solar masses of oxygen. This high level of oxygen production is significant, as it highlights the capacity of supernovae to generate the necessary building blocks for water.
The next step in the research was to determine how this oxygen would behave in the surrounding environment. As the gas from the supernova cooled, it mixed with the hydrogen that had been left behind by the dying star. These interactions between hydrogen and oxygen led to the formation of water in the dense clumps of gas and dust remaining from the explosion. These clumps, or molecular clouds, would eventually collapse to form new generations of stars and planets, making them potential sites for future water-rich environments.
In their simulations, Whalen and his team found that water began to form in these clumps within 30 to 90 million years after the supernova event in the case of the smaller star (13 solar masses). The amount of water produced during this period ranged from one hundred millionth to one millionth of a solar mass. For the larger star, the process was quicker, with water production reaching approximately 0.001 solar masses after just 3 million years.
This discovery is particularly significant because it suggests that water may have formed in the universe much earlier than previously thought, during the very early stages of galaxy formation. If water could survive the destructive processes associated with the birth of the first galaxies—processes that involve high-energy collisions and intense radiation—it could have played a crucial role in the formation of planets in the early universe. Water is essential for the development of habitable environments, so the presence of water in the earliest stages of galaxy formation could increase the likelihood that planets capable of supporting life existed long before the Earth itself.
The research also provides new insights into the role of supernovae in the chemical evolution of the universe. Supernovae are responsible for dispersing heavy elements, such as oxygen, into space, enriching the interstellar medium and providing the materials necessary for the formation of stars and planets. The ability of these explosions to produce oxygen and subsequently facilitate the formation of water suggests that supernovae may have played a key role in the creation of the first habitable environments.
While the exact timeline for the formation of water in the early universe is still a subject of ongoing study, the findings of this research highlight the importance of water as a potentially early and crucial constituent of the first galaxies. The fact that water could have been present just 100 to 200 million years after the Big Bang provides new clues about the conditions that may have been necessary for the emergence of life in the universe.
Moreover, this study opens the door for future research into the survival and role of water in the primordial cosmos. If water could withstand the tumultuous processes associated with the formation of the first galaxies, it may have persisted in some form during the formation of the first stars and planetary systems. This provides a tantalizing possibility that life, or at least the conditions conducive to life, might have emerged in the universe much earlier than we currently envision.
The discovery that water may have been a part of the first galaxies is a significant step forward in our understanding of the cosmos. It suggests that the universe, even in its earliest moments, may have been a far more complex and life-friendly environment than previously imagined. As our models of the early universe continue to improve and our ability to study distant galaxies advances, we may find even more evidence that water—and the conditions necessary for life—may have been present in the universe long before the formation of the Earth. This has profound implications not only for the study of cosmic history but also for the search for life beyond our planet. The presence of water in the early universe suggests that life could exist elsewhere, in regions of space we have yet to explore, and that the fundamental building blocks for life could be widespread throughout the cosmos.
More information: D. J. Whalen et al, Abundant water from primordial supernovae at cosmic dawn, Nature Astronomy (2025). DOI: 10.1038/s41550-025-02479-w