FAST telescope and DESI collaboration reveals cosmic gas dynamics
A joint observation by China's FAST radio telescope and the international DESI spectrograph indicates that the universe's declining star formation rate is not due to a lack of fuel, but a reduced capacity to process gas.
An international research team, utilizing China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the Dark Energy Spectroscopic Instrument (DESI), has produced new measurements of neutral hydrogen evolution over the past 4.5 billion years. The findings, published in Nature Astronomy, challenge previous assumptions about why star formation in the universe has slowed down.
The study found that while the rate of star formation has significantly decreased, the reserves of neutral hydrogen gas have not diminished proportionally. This contradicts a popular explanation that star formation declines because the cold gas needed to form stars is depleted.
Researchers combined FAST's high sensitivity with DESI's large-scale spectroscopic survey data to analyze approximately 2.5 million galaxies. By stacking weak signals from neutral hydrogen, detected via its 21 cm radio line, they were able to trace its abundance with unprecedented statistical accuracy.
The measurements reveal that the star formation rate 4.5 billion years ago was about 2.5 times higher than today, while the density of neutral hydrogen was only about 1.4 times higher. Scientists propose that the issue is not a lack of gas, but a reduced efficiency in converting neutral hydrogen into molecular hydrogen, the direct precursor for star formation. This suggests the universe has ample gas, but its ability to form stars has become less efficient over time.