First glimpse of primordial matter

The well-established theory of Big Bang nucleosynthesis (BBN) asserts that only hydrogen, helium, and a trace of lithium were created in the first few minutes of the cosmos. The creation of all heavier nuclei requires stars, which first appeared several hundred million years later. Now a team of astrophysicists at the University of California, Santa Cruz, has used high-sensitivity absorption spectroscopy at the 10-meter Keck-I telescope in Hawaii to discover two intergalactic gas clouds with no trace of heretofore ubiquitous carbon, oxygen, or any other nonprimordial element. The team examined cosmologically distant clouds by looking at the absorption lines their ingredients cut into the continuum emission spectra of background quasars seen through the clouds. The high redshifts (z ≈3.3) of the two apparently pristine clouds found by the team date them to about 2 billion years after the Big Bang, when most first-generation stars had already spewed out lots of heavy nuclei in supernovae. The discovery therefore bespeaks a surprisingly inhomogeneous dispersal of the products of early stellar nucleosynthesis. The deuterium component in one of the clouds has yielded the first measurement of the ²H/¹H isotopic abundance ratio—a key BBN parameter—in a system seemingly uncontaminated by stellar ejecta. The measured ratio agrees well with the BBN prediction based on cosmic-microwave-background data. (M. Fumagalli, J. M. O’Meara, J. X. Prochaska, Science 334, 1245, 2011 .)—Bertram Schwarzschild