The decline and fall of stars in the Universe

"Clumps of matter grow via gravity, drawing more and more mass into them. Eventually, they become so massive that they collapse, triggering new stellar birth. At early times, star-formation was rare, occurring only in massive, fast-growing regions. Slightly later, growth by mergers and accretion causes star-formation rates to steadily rise. After ~3 billion years, stars form at the fastest rate of all-time: what astronomers call "cosmic noon.""

"The expanding Universe drives galactic groups and clusters apart. Cosmic mergers become rarer, occurring only within bound systems. Mass accretion becomes less significant, as the intergalactic medium dilutes. Even within galaxies, ongoing star-formation depletes the gas necessary to create new stars. The Euclid mission confirmed star-formation's decline across the past several billion years. Now, 13.8 billion years after the Big Bang, new stars are uncommon. Today's star-formation rate, merely 3% of what it was at cosmic noon, continues to drop."

Initially the Universe contained no stars; matter first collected into clumps that grew by gravity, accreting mass until regions became massive enough to collapse and ignite star formation. In the earliest epoch star formation was rare and confined to the most massive, rapidly growing regions. Mergers and accretion then increased growth, raising star-formation rates until about three billion years after the Big Bang, when the cosmic star-formation rate peaked at 'cosmic noon.' After that peak the cosmic expansion reduced mergers and accretion, intergalactic gas diluted, and internal gas reservoirs were depleted, causing star formation to decline to about three percent of its peak.

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