TITLE: "Chemistry and Gas Dynamics in the Dark Ages of the Early Universe"

SPEAKER: Professor Phillip C. Stancil,

TIME: Thursday Sept. 5, 2002 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

The formation of the very first luminous objects (stars and quasars) marks a transformation of the early Universe from a relatively homogeneous expanding gas to the clumpy structure we observe today. This transformation began at a redshift z of about 30. Another transformation occurred at a much earlier time when the Universe was only about 100,000 years old (z~1400) known as Recombination. Prior to Recombination, the Universe was completely ionized and photons, the cosmic background radiation (CBR), interacted strongly with the ionized matter. At Recombination, electrons and protons combined to form neutral hydrogen and the Universe evolved to a mostly neutral state. The resulting neutral gas was also transparent to the CBR so that the photons free-streamed until today, resulting in the 2.7K cosmic microwave background (CMB). Measurements of the CMB are therefore direct probes of the state of the early Universe at Recombination. However, there are no measurements at later times until quasars are observed, with the current record-holder being at z=6.28. The intervening time is therefore known as the Dark Ages and can currently only be explored through theory and numerical simulations. I will discuss numerical simulations of the evolution of the early Universe from Recombination to the formation of the first stars. In particular, the important role of molecules and uncertainties in chemistry will be addressed. Some proposals for actually making observations of the Dark Ages will be given.