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Beyond Earthly Skies

Extreme Outliers of the Milky Way

12 Jul 2014, 22:00 UTC
Extreme Outliers of the Milky Way
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The Milky Way contains a population of a few hundred billion stars. Like any galaxy, the Milky Way does not have a well defined “edge”. As one moves away from the galaxy, the number of stars per given volume of space simply becomes ever so vanishingly small. Bochanski et al. (2014) report on the discovery of two of the most distant Milky Way stars known to date. The two stars are given the identifiers - ULAS J0015+01 and ULAS J0744+25. Both stars were bright enough to be detectable because they have entered their final stages of stellar evolution and have swelled into red giants, resulting in a considerable increase in their luminosities.ULAS J0015+01 and ULAS J0744+25 have large estimated distances of 274 ± 74 kpc and 238 ± 64 kpc, respectively, making them the first two Milky Way stars found beyond 200 kpc. For comparison, the disk of the Milky Way, which contains the majority of the galaxy’s stars, is approximately 30 kpc, or 100,000 light-years in diameter. ULAS J0015+01 and ULAS J0744+25 are also moving away from the Milky Way’s centre at 52 ± 10 km/s and 24 ± 10 km/s, respectively.A number of possible scenarios have been considered ...

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