Cosmic Star Formation Decline Linked to Gas Cycle Efficiency

• Astronomers have observed that the rate of star formation in the universe has plummeted over the last 4.5 billion years, but the cause is not a simple lack of hydrogen fuel.
• Research using the FAST telescope and DESI data reveals that while star formation rates dropped by 2.5 times, neutral atomic hydrogen (HI) levels decreased by only 1.4 times.
• The decline in star birth is attributed to issues in the "baryon cycle" rather than a total fuel depletion.

Key Findings

• Approximately 4.5 billion years ago, star formation was significantly more active than today.
• While the global supply of neutral hydrogen remains relatively stable, the conversion of this gas into molecular hydrogen (H2)—the necessary fuel for stars—has become inefficient.
• This discrepancy suggests that the mechanisms pulling matter into galaxies or replenishing gas supplies are failing as the universe ages.

Context and Implications

• The study focuses on the "late-time phase" of cosmic star formation, which peaked about 10 billion years ago during "cosmic noon."
• Findings indicate that star birth is limited not by the presence of hydrogen, but by the galaxy-scale processes that regulate its transition into usable star-forming material.
• Future investigations aim to look beyond the current 7.2-billion-year observational limit of the FAST telescope to understand earlier stages of galaxy evolution.