Detection of Pristine Gas Two Billion Years after the Big Bang

In the current cosmological model, only the three lightest elements were created in the first few minutes after the Big Bang; all other elements were produced later in stars. To date, however, heavy elements have been observed in all astrophysical environments. We report the detection of two gas clouds with no discernible elements heavier than hydrogen. These systems exhibit the lowest heavy-element abundance in the early universe and thus are potential fuel for the most metal poor halo stars. The detection of deuterium in one system at the level predicted by primordial nucleosynthesis provides a direct confirmation of the standard cosmological model. The composition of these clouds further implies that the transport of heavy elements from galaxies to their surroundings is highly inhomogeneous.Comment: 32 pages, 11 figures, SOM included. To appear in Scienc

Growth curves for algebras

This paper studies matrix representations of algebras (over a field) using countably-infinite matrices which are both row and column finite, and in which the bandwidth growth is controlled. The ideas lead naturally to a concept of "growth of an algebra", somewhat analogous to the growth associated with GK-dimension. They also lead in a similar way to a dimension function on general algebras, which we term bandwidth dimension. For each real number r ∈ [0,1], we construct an algebra having bandwidth dimension precisely r. Since the free algebra turns out to have bandwidth dimension 0, our new dimension promises to distinguish among algebras of infinite GK-dimension