Cosmic star formation decline research

An international research team, including the Chinese Academy of Sciences, has published findings in Nature Astronomy that challenge existing theories regarding the decline of cosmic star formation.

By analyzing approximately 2.5 million galaxies using data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the Dark Energy Spectroscopic Instrument (DESI), scientists identified a discrepancy between the rate of star formation and the availability of neutral hydrogen. While the cosmic star formation rate has decreased by a factor of approximately 2.46 over the last 4.5 billion years, the density of neutral atomic hydrogen has only declined by a factor of about 1.35 to 1.4.

These results suggest that the slowdown in stellar production is not caused by a depletion of raw hydrogen material. Instead, the research indicates the decline may stem from a decreasing efficiency in converting neutral hydrogen into the dense molecular gas required to fuel star birth. To reach these conclusions, researchers utilized HI spectral stacking to combine faint radio signals from millions of galaxies, overcoming the difficulty of detecting weak 21-centimeter emissions from distant sources.