This stream is not in the plane of the Milky Way galaxy and is likely a remnant of an ancient dwarf satellite galaxy, long since disrupted and assimilated into the Milky Way. It consists of old stars deficient in heavy elements.
Research from the Radial Velocity Experiment at the Australian Astronomical Observatory headed by Quentin Parker was first to quantify the nature of the stream, though astronomers had known of its existence for some time. It was first discovered in 1971.
- Ibata, Rodrigo; Gibson, Brad (April 2007). "The Ghosts of Galaxies Past". Scientific American 296 (4): 40–45. doi:10.1038/scientificamerican0407-40. PMID 17479629.
- Eggen, Olin (1971). "The Arcturus Group". Publications of the Astronomical Society of the Pacific 83 (493): 271–85. Bibcode:1971PASP...83..271E. doi:10.1086/129120.
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