Two gas clouds containing pristine samples of the gas spawned
by the Big Bang has been spotted by astronomers.
Using the powerful, Hawaii-based Keck I telescope, University of California Santa Cruz graduate student Michele Fumagalli and his colleagues focused on two distant quasars, called J1134+5742 and Q0956+122. Quasars are intense light sources produced by superheated matter falling into massive black holes at the centres of galaxies. To reach Earth, the light from them has to pass through any clouds of gas that are in their paths.
By looking at the light that arrives, researchers can work out what is in the gas because different chemical elements absorb discrete wavelengths of light, producing a unique chemical fingerprint. But prior to now all of the gas clouds that have ever been reported have always shown signs of significant contamination with metals. These can only have come from early stars, which produce heavier elements by fusing lighter substances, like hydrogen, together.
This means that the compositions of these contaminated gas clouds cannot be relied upon to test theories about the Big Bang, and the sorts of elements and in what ratios, it produced. Current models of the Big Bang suggest that, after about 8 minutes, the newborn Universe cooled from a sizzling one billion Kelvin to about 500 million Kelvin, which is hot enough for new elements to be born and yet cool enough for them to be stable.
The result, theoreticians think, was a mixture comprising mainly hydrogen and its isotope deuterium, together with a bit of helium and a trace of lithium. Yet without some of the resulting gas to study, the model remained unsupported by experimental evidence.
But the new findings, which are published this week by the journalScience揭示气体云,追溯到大约billion years after the Big Bang and are devoid of any metal contamination, change all that.
"The lack of metals tell us this gas is pristine," says Fumagalli. "It's quite exciting because it's the first evidence that fully matches the composition of the primordial gas predicted by the Big Bang theory."
Apart from validating existing hypotheses, the new findings also shed light on how the early galaxies were forming. Theoretical models predict that these nascent galaxies were growing by pulling in massive streams of cold gas, but these "cold flows" as they are known, have never been seen. Fumagalli is speculating that the pristine clouds he has spotted might just be them...
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