Described in a paper that appears today in the journal Nature Astronomy, the discovery means habitable exoplanets could have started forming much earlier — before the first galaxies formed and billions of years earlier than was previously thought.
This artist’s impression shows the evolution of the Universe beginning with the Big Bang on the left followed by the appearance of the Cosmic Microwave Background. The formation of the first stars ends the cosmic dark ages, followed by the formation of galaxies. Image credit: M. Weiss / Harvard-Smithsonian Center for Astrophysics.
“Before the first stars exploded, there was no water in the Universe because there was no oxygen,” said University of Portsmouth astronomer Daniel Whalen.
“Only very simple nuclei survived the Big Bang — hydrogen, helium, lithium and trace amounts of barium and boron.”
According to Dr. Whalen and his colleagues, water molecules began forming shortly after the first supernova explosions, known as Population III supernovae.
These cosmic events, which occurred in the first generation of stars, were essential for creating the heavy elements — such as oxygen — required for water to exist.
“Oxygen, forged in the hearts of these supernovae, combined with hydrogen to form water, paving the way for the creation of the essential elements needed for life,” Dr. Whalen said.
In their study, the researchers examined two types of supernovae: core-collapse supernovae, which produce a modest amount of heavy elements, and the much more energetic Pop III supernovae, which eject tens of solar masses of metals into space.
They found that both types of supernovae formed dense clumps of gas enriched with water.
While the overall amount of water produced in these early supernovae was modest, it was highly concentrated in dense regions of gas, known as cloud cores, which are thought to be the birthplaces of stars and planets.
These early water-rich regions likely seeded the formation of planets at cosmic dawn, long before the first galaxies took shape.
“The key finding is that primordial supernovae formed water in the Universe that predated the first galaxies,” Dr. Whalen said.
“So water was already a key constituent of the first galaxies.”
“This implies the conditions necessary for the formation of life were in place way earlier than we ever imagined — it’s a significant step forward in our understanding of the early Universe.”
“Although the total water masses were modest, they were highly concentrated in the only structures capable of forming stars and planets.”
“And that suggests that planetary discs rich in water could form at cosmic dawn, before even the first galaxies.”
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