A Star is Born

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Science  04 Apr 2003:
Vol. 300, Issue 5616, pp. 19-21
DOI: 10.1126/science.300.5616.19e

The first billion years of the universe [redshift (z) greater than 6] was a time of great darkness and commotion. After inflation, there was mostly hydrogen and helium gas expanding into darkness. Residual ionization and primordial density fluctuations from the Big Bang led to clumping of this molecular gas and dark matter. The first sources of light, probably stars or quasi-stellar objects (QSOs), began to form around z ∼ 30, and most of the hydrogen was reionized by z ∼ 7. Observers are beginning to discover some of the earliest QSOs (z ∼ 6), and these ancient objects provide the most luminous markers for checking models of the formation of the early universe.

Using the Hubble Space Telescope, Freudling et al. have obtained near-infrared spectra of three QSOs (5.7 < z < 6.3). The Fe/Mg abundance ratios are similar to or greater than that of the Sun, suggesting that massive galaxies (as opposed to galaxy mergers) with solar or supersolar Fe/Mg appeared within the first billion years. If the QSOs were triggered by supernovae, then it would have taken 0.5 to 0.8 billion years from the formation of the supernovae progenitors for the gas to become enriched enough to supply solar or supersolar Fe/Mg. Formation of the progenitors at z ∼ 30 to 10 would be consistent with recent results from the Wilkinson Microwave Anisotropy Probe, indicating that star formation began about 0.2 billion years after the Big Bang.—LR

Astrophys. J.587 Rapid Release 21 March 2003 (astro-ph/0303424).

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