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We describe results from a fully self-consistent three-dimensional
hydrodynamical simulation of the formation of one of thefirst stars in
the Universe. In current models of structure formation,dark matter
initially dominates, and pregalactic objects formbecause of
gravitational instability from small initial densityperturbations. As
they assemble via hierarchical merging, primordialgas cools through
ro-vibrational lines of hydrogen molecules andsinks to the center of
the dark matter potential well. The high-redshiftanalog of a molecular
cloud is formed. As the dense, central partsof the cold gas cloud
become self-gravitating, a dense core of~100
M (where
M is the mass of the
Sun) undergoesrapid contraction. At particle number densities greater
than 109 per cubic centimeter, a 1 M protostellar core
becomes fullymolecular as a result of three-body H2
formation. Contrary toanalytical expectations, this process does not
lead to renewedfragmentation and only one star is formed. The
calculation isstopped when optical depth effects become important,
leaving thefinal mass of the fully formed star somewhat uncertain. At
thisstage the protostar is accreting material very rapidly
(~102M
year1). Radiative feedback from the star will not only
halt its growthbut also inhibit the formation of other stars in the
same pregalacticobject (at least until the first star ends its life,
presumablyas a supernova). We conclude that at most one massive
(M 1 M)metal-free star forms per pregalactic halo, consistent with recentabundance measurements of metal-poor galactic halo stars.
1 Harvard Smithsonian Center for Astrophysics,
Cambridge, MA 02138, USA.
2 Institute of Astronomy,
University of Cambridge, Cambridge CB3 0HA, UK.
3 Astrophysics Division, Department of Physics,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
4 Center for Astrophysics & Space Sciences,
University of California, San Diego, La Jolla, CA 92093, USA.
(where
M
2 M
1 M
