Pure Clouds From the Big Bang
November 11, 2011 Leave a comment
For the first time, astronomers have discovered clouds of gas that apparently do not contain any elements created by stars – they exist as they were created minutes after the Big Bang. Or at least they did about 12 billion years ago, since they’re about 12 billion light years away – but that’s still 2 billion years after the Big Bang.
Just after the Big Bang, nuclear reactions created the three lightest elements – hydrogen, helium, and a tiny bit of lithium. Stars then converted some of this material into the heavy elements such as carbon and oxygen that pepper the cosmos today.
But no-one has ever seen a star or gas cloud made solely of these three Big Bang elements. Instead, all known stars and gas clouds harbour at least some “metals”, the term astronomers use to describe any element, even carbon and oxygen, that is heavier than helium…
Now, Michele Fumagalli and Xavier Prochaska of the University of California, Santa Cruz and John O’Meara of Saint Michael’s College in Vermont, have found two pristine gas clouds. “Their chemical composition is unusual,” says Fumagalli. “This gas is of primordial composition, as it was produced during the first few minutes after the Big Bang.”
… The clouds are far too faint to observe directly. Fumagalli and colleagues discovered them only because the clouds happen to lie in front of even more distant quasars, which are luminous galaxies that were much more common long ago. Atoms in the gas clouds absorb some of the light from the background quasars, and the wavelengths at which absorption is evident reveals important information about the composition of the clouds…
Despite using the mammoth Keck I telescope atop Mauna Kea in Hawaii, the astronomers failed to find any element except hydrogen in the two clouds. While the researchers also expect helium and lithium to be present, their technique is not sensitive to those elements. However, if oxygen, carbon or silicon were present, it should have been easy to spot…
“It’s a very interesting discovery,” says Nick Gnedin, an astronomer at Fermilab in the US, who is unaffiliated with the discovery team. Gnedin says it has been very difficult to understand why all other gas clouds – even those at greater distances – contain metals. These newfound exceptions should help astronomers understand why all other gas clouds contain metals, he says…
In addition to ordinary hydrogen, Fumagalli and colleagues detected the hydrogen isotope deuterium in the Ursa Major cloud. Physicists believe that the Big Bang produced deuterium but that stars then destroyed it – so the universe once had more deuterium than it does today.
(I briefly talked about isotopes in an earlier post: the difference between deuterium and normal hydrogen is that deuterium has a neutron in addition to a normal hydrogen atom’s proton and electron. Deuterium exists in nature still, but in relatively small amounts.)
The high deuterium-to-hydrogen ratio in the gas matches Big Bang predictions. “The fact that we see deuterium that is comparable to what is expected from theory is giving us more confidence that this gas is actually primordial in its composition,” says Fumagalli.
This discovery is pretty interesting, and I would bet that studying these clouds and others like them will teach us a lot about the ancient universe. I will prepare myself for future bombshells.
This isn’t a particularly relevant place to say it, but it still boggles my mind that we can detect things from that far away, and consequently from that long ago. Astronomers time travel further back than any science fiction writer could’ve imagined – and I suppose we do too when we look into the sky, to a lesser degree. We take it for granted now, but it’s truly incredible.
Update: For a very enthusiastic explanation of why the elemental composition of these clouds is predicted by the Big Bang, check out this article from Starts With a Bang.