Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Anirudh Chiti, Anirudh Chiti, , ,
| Summary:
Stars that contain only trace amounts of elements heavier than helium,
referred to as having low "metallicity", preserve the chemical fingerprints of
the first generation of stars and supernovae. In the Milky Way, the lowest
metallicity stars show an extreme over-abundance of carbon relative to other
elements, which has been hypothesized to be a unique result of the first
low-energy supernovae. However, the origin of this signature has remained a
mystery, since no such stars have been discovered in the ancient dwarf galaxies
where they are thought to have formed. Here, we present observations of a star
in the >10 billion year old ultra-faint dwarf galaxy Pictor II, that shows the
lowest iron and calcium abundances outside the Milky Way (<1/43,000th solar and
~1/160,000th solar), with a factor of >3000x relative carbon enhancement. As
the first unambiguous second-generation star in a relic dwarf galaxy, this
object demonstrates that carbon-enhanced second-generation stars can originate
in primordial small-scale systems. This star supports the hypothesis that
carbon-enhancement is produced by low-energy-supernovae, since the yields of
energetic supernovae are harder to retain in small-scale environments. This key
local signature of chemical enrichment by the first stars traces a regime
inaccessible to current high-redshift observations, which cannot detect the
early enrichment of the smallest galaxies.
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