SDSS J102915+172927

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SDSS J102915+172927
SDSS J102915 172927.jpg
SDSS J102915 172927 as seen by ESO - VLT
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Leo
Right ascension 10h 29m 15.15s
Declination 17° 29′ 28″
Apparent magnitude (V) +16.92

SDSS J102915+172927 or Caffau's star is a population II star in the galactic halo, seen in the constellation Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy.[1] At the time of its discovery, it had the lowest metallicity of any known star.[2] It is small (less than 0.8 solar masses),[3] deficient in carbon, nitrogen, oxygen, and completely devoid of lithium. Because carbon and oxygen provide a fine structure cooling mechanism that is critical in the formation of low-mass stars, the origins of Caffau's star are somewhat mysterious. It has been suggested, both for theoretical and observational reasons, that the formation of low-mass stars in the interstellar medium requires a critical metallicity somewhere between 1.5×10−8 and 1.5×10−6.[4] The metallicity of Caffau's star is less than 6.9×10−7.[4] According to Schneider et al., cooling by dust rather than the fine structure lines of CII and OI may have enabled the creation of such low-mass, metal-poor stars in the early universe.[3][5] The absence of lithium implies past temperatures of at least two million Kelvins.[4]

The star was described by Elisabetta Caffau et al. in an article published by the journal Nature in September 2011. Caffau had been searching for extremely metal-poor stars for the past ten years.[6] It was identified by automated software which analyzed data from the Sloan Digital Sky Survey. This was followed up by observations with the X-shooter and UVES instruments on the Very Large Telescope in Chile.[2] Caffau and her team expect to find between five and fifty similar stars with the telescope in the future.[5]

See also[edit]

Ultra low metallicity / ultra metal poor stars


  1. ^ Lemonick, Michael D. (2011-09-06). "Cosmic Anomaly: The Star That Shouldn't Exist". TIME. Retrieved 2012-08-20. 
  2. ^ a b "The Star That Should Not Exist". ESO. 2011-08-31. Retrieved 2012-08-20. 
  3. ^ a b Schneider, Raffaella; et al. (2012-03-19). "The formation of the extremely primitive star SDSS J102915+172927 relies on dust". arXiv:1203.4234Freely accessible. 
  4. ^ a b c Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; et al. (1 September 2011). "An extremely primitive star in the Galactic halo". Nature. 477 (7362): 67–69. Bibcode:2011Natur.477...67C. PMID 21886158. arXiv:1203.2612Freely accessible. doi:10.1038/nature10377. Retrieved 7 September 2012. 
  5. ^ a b Doyle, Amanda (2011-09-01). "A forbidden star". Retrieved 2012-08-20. 
  6. ^ Redd, Nola Taylor (2011-08-31). "Impossible Star Defies Astronomers' Theories". Retrieved 2012-08-20.