Astronomer Dr Robert Braun of the CSIRO Astronomy and Space Science in Australia has discovered that today’s Universe contains more atomic hydrogen gas than previously thought. A new study provides the first accurate measurement of this gas in galaxies close to our own.
Dr Braun analyzed data for M31, M33, LMC galaxies, obtained with CSIRO's Parkes and Australia Telescope Compact Array telescopes in New South Wales and other radio telescopes in the USA and the Netherlands. Image shows M31, or the Andromeda Galaxy, our Milky Way's largest galactic neighbor (NASA/JPL-Caltech)
Just after the Big Bang the Universe’s matter was almost entirely hydrogen atoms. Over time this gas of atoms came together and generated galaxies, stars and planets — and the process is still going on. Astronomers want to understand where, when and how the atomic gas is transformed to better understand the Universe in which we live.
Image shows neutral hydrogen density in the inner disk of the Andromeda Galaxy (R. Braun)
By taking a new look at some archival data, Dr Braun has found that galaxies around us are hiding about a third more atomic hydrogen gas than previously calculated. The finding will appear in the Astrophysical Journal.
The research also shows that the gas is distributed very differently from how it was in the past, with much less in the galaxies’ outer suburbs than billions of years ago.
“This means that it’s much harder for galaxies to pull the gas in and form new stars,” Dr Braun said. “It’s why stars are forming 20 times more slowly now than in the past.”
The new finding doesn’t help solve the problem of “dark matter” – lots of mass, detectable by its gravity, that haven’t been yet identified.
“Even though there’s more atomic hydrogen than we thought, it’s not a big enough percentage to solve the dark matter problem. If what we are missing had the weight of a large kangaroo, what we have found would have the weight of a small echidna,” Dr Braun explained.
Nevertheless, the work will continue to feed into our understanding of how galaxies evolve over time.
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Bibliographic information: Braun, R. 2012. Cosmological evolution of atomic gas and implications for 21 cm H I absorption. Manuscript accepted for publication in the Astrophysical Journal. ArXiv:1202.1840v1
