Finding the universe’s first water could change life’s beginnings.

• A study published in Nature Astronomy suggests that the universe’s oldest stars became water sources as their nuclear fires were extinguished in massive supernovae.
• The first stars were born a few hundred million years after the Big Bang, when all visible matter comprised primordial hydrogen and helium atoms.
• The stars’ nuclear furnaces were powered by hydrogen, and as they shone, they heated up the surrounding intergalactic gas and dust.
• When the stars ran out of hydrogen to burn, they blew up as supernovae, ionising the interstellar medium around them, setting the stage for the formation of new stars and triggering a cycle of star births in perpetuity.
• The longevity of a star depends on its mass, with more massive stars dying faster as more heat is released.
• The universe’s oldest stars form population III: massive stars composed completely of hydrogen and helium, which are believed to be the stellar nurseries where water must have first appeared in the cosmos.
• The conditions required to create water existed around the same time when those first supernovae lit up the cosmos: sometime between 50 million and 1 billion years after the Big Bang.
• The oxygen produced in these supernovae combined with hydrogen to create water, which is crucial for forming the elements necessary for life.
• The earliest stars could not have possibly engendered water in the universe before they became supernovae, as the supernovae have to expel oxygen, which only forms during late stages of nuclear burning in massive stars that are destined to explode.
• The study suggests that the first supernovae themselves produced enough water to drench the infant universe, implying that planets could have formed even before the first galaxies were born.
• The findings validate previous research that at least some of Earth’s water was delivered by comets early in the planet’s history and confirm that water molecules remain unchanged from their interstellar origins as they reach planets elsewhere in the universe.