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An extremely primitive star in the Galactic halo
Elisabetta Caffau1, Piercarlo Bonifacio, Patrick François
1Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany. Elisabetta.Caffau@obspm.fr
Nature
|September 3, 2011
Summary
This study found that low-mass stars can form even in the early Universe with very low metallicity. This challenges previous theories and suggests these stars experienced high temperatures, leading to lithium depletion.
Area of Science:
- Astronomy and Astrophysics
- Cosmic Chemical Evolution
- Stellar Formation
Background:
- The early Universe's composition was primarily hydrogen and helium, with heavier elements synthesized later in stars.
- Metallicity (Z) is the mass fraction of elements heavier than helium, crucial for understanding stellar evolution.
- Previous theories suggested a critical metallicity threshold for low-mass star formation, though debated.
Purpose of the Study:
- To investigate the formation of low-mass stars in environments with extremely low metallicity.
- To challenge the existing theoretical constraints on star formation in the early Universe.
- To analyze the chemical composition and lithium depletion in a very metal-poor star.
Main Methods:
- Analysis of the chemical composition of a star in the Galactic halo.
- Measurement of the star's metallicity (Z) and abundance of specific elements (carbon, nitrogen, oxygen).
- Assessment of lithium abundance to infer thermal history.
Main Results:
- A star with very low metallicity (Z ≤ 6.9 × 10⁻⁷) was identified.
- The star exhibited a chemical pattern typical of extremely metal-poor stars, lacking enrichment in carbon, nitrogen, and oxygen.
- No lithium was detected, consistent with lithium depletion at high temperatures.
Conclusions:
- Low-mass stars can form at metallicities below previously suggested critical values.
- The findings challenge existing models of early star formation and chemical enrichment.
- Observed lithium depletion indicates the star's material experienced temperatures exceeding two million Kelvin.
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