🌊 Abundant water from primordial supernovae at cosmic dawn

• Researchers have discovered that the first water in the universe formed in Population III supernovae approximately 100-200 million years after the Big Bang.
• Dense molecular cloud cores in supernova remnants proved to be the primary sites of water production, with concentrations almost as high as in our solar system today.
• These water-rich, dense cloud cores may also be sites where protoplanetary disks and planets formed early in the universe's history.

Water formation in the universe's first explosions

New numerical simulations conducted by researchers from Portsmouth University and United Arab Emirates University show that water formed as early as 13.5 billion years ago in the first supernova explosions. The researchers modeled explosions of Population III stars (the universe's first generation of stars) with masses of 13 and 200 solar masses.

When these early stars exploded as supernovae, heavy elements were ejected into space, including oxygen with masses of 0.051 and 55 solar masses for the two simulated explosions. In the expanding explosion remnant, the oxygen reacted with hydrogen and hydrogen gas (H₂) to form water.

"Diffuse water vapor later permeated both galaxy clusters with mass fractions of 10⁻¹⁴ to 10⁻¹² in core-collapse supernovae and 10⁻¹² to 10⁻¹⁰ in pair-instability supernovae," the researchers explain in the study published in Nature Astronomy.

Cloud cores: the cradle of water

The largest amounts of water, however, were not formed in the diffuse gas but in dense cloud cores that were contaminated by metals from the explosions and then collapsed to high densities. In these environments, the rate of water formation increased dramatically.

In pair-instability supernovae, water masses increased sharply from 10⁻⁶ solar masses to 10⁻³ solar masses in just 3 million years. In core-collapse supernovae, the amount rose from 10⁻⁸ solar masses to 10⁻⁶ solar masses over 30-90 million years.

The cloud cores reacted differently to the explosions depending on their metallicity. The researchers explain: "The pair-instability supernova core becomes self-gravitating much earlier than in core-collapse supernovae because its higher metallicity results in faster cooling and collapse."

Planets already at the dawn of the universe?

A fascinating conclusion from the study is that these dense, dusty cores may also have been sites where planets formed. The numerical simulations show that the gas clump from core-collapse supernovae could produce protoplanetary disks that fragment into Jupiter-like planets.

The higher metal content in the pair-instability supernova core could potentially lead to the formation of rocky planetesimals in protoplanetary disks with low-mass stars. In fact, Jeans masses (minimum mass for gravitational collapse to occur) fell to 1-2 solar masses in the center of the pair-instability supernova core.

Simulations show that these disks were heavily enriched with primordial water, to mass fractions that were 10-30 times greater than in diffuse clouds in the Milky Way in the core-collapse supernova's core and only a factor of a few times lower than in the solar system today in the pair-instability supernova's core.

Water in the first galaxies

The researchers conclude that water was present in primordial-related galaxies due to its earlier formation in their constituents. Water mass fractions in diffuse supernova remnants could reach 10⁻¹⁰, only one order of magnitude less than in the Milky Way today.

Some of this water would have been photodissociated by massive stars in these galaxies or destroyed through other chemical reactions. But increasing dust fractions in early galaxies would also have protected water from ultraviolet radiation and reduced its destruction.

The research findings suggest that a fundamental ingredient for life was in place in the universe earlier than previously thought, and that water was likely a key component in the first galaxies.

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