Evrim Yazgin
Cosmos science journalist
Computer simulations suggest that water first appeared in the universe just 100–200 million years after the Big Bang, far earlier than previously believed.
The findings, published in Nature Astronomy, imply that water – crucial for life – may have been a key ingredient in the formation of the first galaxies. It also suggests that habitable planets suitable for life could have formed very early in the history of the universe.
Water, H2O, forms when 2 hydrogen atoms bond to 1 oxygen atom. So, before you can have water molecules, you need the atoms first.
According to cosmologists’ best theories of the universe, the first atomic nuclei formed just minutes after the Big Bang. But it took another 380,000 years for the universe to cool down enough for electrons to be trapped in orbits around the nuclei to form the first atoms.
The first atoms were hydrogen and helium, with 1 and 2 protons in their nuclei respectively.
Oxygen and other heavier elements weren’t in the picture until the formation of the first stars, which could fuse hydrogen and helium nuclei in their cores or explode in a supernova to make larger nuclei.
So, water would have formed for the first time after this.
The first stars, known as Population III stars, are thought to have formed from clouds of gas 150–200 million years ago.
In this new study, a team of astrophysicists simulated two supernovae: one for a Population III star 13 times the mass of our Sun – a core-collapse (CC) supernova – and the other for a star 200 times bigger than the Sun – a pair-instability (PI) supernova.
The amount of oxygen created in the simulations were 0.051 and 55 times the mass of the Sun respectively. The simulations showed that the oxygen cooled and mixed with surrounding material to form water.
These clumps of dense material were likely to be the best place for second-generation stars and planets to form.
Water formed in the first simulation reached one-millionth of the mass of the Sun 30–90 million years after the supernova. A thousand times that amount of water was produced within just 3 million years of the second supernova explosion.
The authors suggest that some of this primordial water may have survived the potentially destructive process of galaxy formation to form planets with water billions of years ago.
“The large H2O mass fractions and the potential for low-mass star formation in the PI supernova core raise the possibility of a habitable zone in the protoplanetary disk in which equilibrium temperatures allow water to exist in liquid form,” they write.
