International scientists uncover reason behind slowdown in star formation
The latest observations indicate that whilst neutral hydrogen is abundant, the process by which gas is converted into stars has slowed down, altering our understanding of galaxy evolution
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Photo source: m-gucci / iStock
An international team of astronomers led by the Chinese Academy of Sciences analysed data collected by the "Chinese Sky Eye" (FAST) and the Dark Energy Spectroscopic Instrument (DESI), covering approximately 2.5 million galaxies across about one-third of the sky. Using spectral line stacking – a technique that combines faint 21-centimetre radio signals from approximately 2.5 million galaxies – the scientists have, for the first time, traced the evolution of neutral atomic hydrogen (the primary fuel for stars) on cosmic timescales with sufficient statistical precision.
According to a report by Science and Technology Daily, a partner of TV BRICS, the results indicate that the star formation rate in the universe 4.5 billion years ago was approximately 2.5 times that of today, whilst the density of neutral atomic hydrogen during the same period was only about 1.4 times that of today. This challenges the long-held assumption that the decline in star formation was solely due to the depletion of cold gas.
As Zhang Chuan-Peng, an associate researcher at the National Astronomical Observatories of the Chinese Academy of Sciences, explained, stars are not formed directly from neutral hydrogen: the gas must first condense into molecular clouds, and the efficiency of this process appears to have declined sharply over the past few billion years.
Guo Hong, the first author of the study and a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, pointed out, "What we are seeing is not a shortage of gas in the universe, but rather that it is becoming increasingly difficult to ‘process’ the gas into stars." This discovery shifts researchers’ focus from gas reserves to the physical conditions affecting the transition of hydrogen from its atomic to molecular state and provides new clues for understanding the phenomenon of reduced star formation in the modern universe.
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