James Webb reveals unexpectedly high activity of early galaxies

New data from the James Webb Space Telescope (JWST) may help explain the unexpectedly high activity of early galaxies in the young Universe, according to a study published in Astronomy & Astrophysics and cited by Space.com, CE Report quotes AGERPRES.

In the first few hundred million years after the Big Bang, the cosmic gas between galaxies was initially cold and dense, later transitioning into a warmer state. This shift is a key clue to how the first galaxies formed and shaped everything we observe today. During this early era, the first stars and galaxies lit up the cosmos like faint lights in the darkness.

The “fuel” for this process was giant clouds of hydrogen gas. Astronomers long suspected these early galaxies were active, but JWST observations reveal them to be brighter, larger, and more intense than previously imagined.

This “cosmic precocity” suggests that current galaxy formation models may need major revision. Traditionally, scientists believed hydrogen clouds collapsed into dark matter halos, cooled, became denser, and then formed stars. However, JWST data indicate a much faster and more aggressive rate of star formation.

To investigate, researchers including Umberto Maio from INAF and Celine Peroux from the European Southern Observatory created advanced simulations called ColdSIM, effectively a “cosmic time machine” to study the first billion years of the Universe.

They found a Universe in rapid transformation. Before the epoch of reionization—when the Universe became transparent to ultraviolet light—the gas was mostly cold and ideal for star formation. But as stars formed and emitted intense UV radiation, the gas quickly became hotter and less dense, fundamentally altering galaxy evolution.

This wasn’t a minor shift—it changed everything about how galaxies grew.

Key findings include:

• Low stellar recycling: Early stars returned less material back into gas clouds after dying
• Fresh gas dominance: New stars formed mostly from unused, primordial gas
• Extremely fast gas consumption: Early galaxies converted gas into stars much faster than modern galaxies

In short, early galaxies were extreme star factories, rapidly consuming gas and producing stars at an intense pace.

The study reshapes our understanding of the early Universe, showing it was far more dynamic and fast-evolving than previously thought.

However, researchers note limitations:

• Simulations cannot fully capture the Universe’s complexity
• Uncertainties remain about star formation processes and chemical conditions (“metals”)
• Models still need refinement to better reflect reality

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