February 7, 2014

Heavy Metal Shapes Early Cosmos

Tiffany Trader
TACC heavy metal gas density graphic

“This is a really exciting time for the field of cosmology. We are now ready to collect, simulate and analyze the next level of precision data…there’s more to high performance computing science than we have yet accomplished,” noted Astronomer and Nobel Laureate Saul Perlmutter in his Supercomputing ’13 keynote address.

In keeping with Perlmutter’s astute observation, astronomers at the University of Texas have made a series of remarkable discoveries using some of the most powerful supercomputers in existence. Massive numerical simulations carried out on Stampede, Lonestar and Ranger (now retired) reveal important details about the early Universe from the Big Bang through the first few hundred million years.

The simulations shed light on how the first galaxies formed, and more specifically, how metals in the stellar nurseries shaped the characteristics of the stars in the first galaxies. Lead researcher Milos Milosavljevic, Associate Professor of Astronomy The University of Texas at Austin, reported the results of this study in the January 2014 edition of the Monthly Notices of the Royal Astronomical Society.

The powerful computational tools provided realistic models of supernova blasts, helping explain the range of metalicity that exists throughout the galaxies. “The universe formed at first with just hydrogen and helium,” Milosavljevic said. “But then the very first stars cooked metals and after those stars exploded, the metals were dispersed into ambient space.”

As the ejected metals fell back into the gravitational fields of the dark matter haloes, they formed the second generation of stars. But the metals dispersed by the early supernovae blasts did not distribute in a uniform pattern.

This incomplete mixing explains the discrepancy in metal distribution in early stars; some were metal-rich others metal-poor.

Another important consideration is the way that the heavier elements emerged from the originating blast. Earlier research assumed the process occurred as a neat spherical blast wave, but the new model suggests that the ejection of metals from a supernova was much more chaotic, with shrapnel shooting in every direction.

Milosavljevic maintains that accurately representing this explosion is “very important for understanding where metals ultimately go.”

In astronomical terms, time translates to distance. In order to see the early universe, astronomers have to peer into the deepest recesses of space, and this takes extremely powerful telescopes. Astronomers are hopeful that we will be able to observe some of these early galaxies with the James Webb Space Telescope (JWST), set to launch in 2018.

One important question surrounding the JWST project is whether to focus on one particular spot or instead employ a mosaic approach to survey a larger area. The lessons learned in this study will be used to guide this strategy.