The role of the first metals in forming the second stars

Britton Smith, Steinn Sigurdsson, Brian O'Shea, Michael Norman

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Numerical simulations of the formation of pop III stars suggest that they were much more massive than the pop II and pop I stars observed today. This is due to the collapse dynamics of metal-free gas, which is regulated by the radiative cooling properties of molecular hydrogen. We study how the collapse of gas-clouds is altered by the addition of metals to the star-forming environment. We perform a series of numerical simulations of pre-enriched star-formation at various metallicities using the adaptive mesh refinement, hydrodynamic + N-body code, Enzo. For metallicities below the critical metallicity, Zcr, collapse proceeds nearly identical to the metal-free case, and only massive, singular objects form. For metallicities well above Zcr, efficient cooling rapidly lowers the gas temperature to the temperature of the cosmic microwave background (CMB), which is significantly higher in the distant past. The gas is physically unable to radiatively cool below the CMB temperature, and thus, becomes very thermally stable. For moderately high metallicities, Z≥10-3.5Z, this occurs early in the evolution of the gas-cloud, when the central density is still relatively low. The resulting cloud-cores show little or no fragmentation, and have mass-scales of a few hundred M. On the other hand, if the metallicity is only slightly above Zcr, the cloud slowly cools without ever reaching the CMB temperature. In this case, the minimum cloud temperature is achieved at much higher densities than in the high-metallicity case, resulting in mass-scales of just a few M.

Original languageEnglish (US)
Title of host publicationFirst Stars III
Number of pages3
StatePublished - 2008
EventFirst Stars III - Santa Fe, NM, United States
Duration: Jul 15 2007Jul 20 2007

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


OtherFirst Stars III
Country/TerritoryUnited States
CitySanta Fe, NM

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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