Squeezing a Cluster from a Dwarf

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Science  16 May 2003:
Vol. 300, Issue 5622, pp. 1055
DOI: 10.1126/science.300.5622.1055b

The ω Centauri globular cluster is the most massive and enigmatic cluster in the Milky Way Galaxy. It contains a mix of metal-poor stars with an east-west elongation and metal-rich stars with a north-south elongation, and it rotates faster than a typical cluster, giving it a more elliptical shape. Most clusters are modeled as forming from mergers of galaxies; however, ω Centauri can be modeled more consistently by capture and accretion.

Two N-body simulations suggest that ω Centauri is the nuclear remnant of a dwarf galaxy that fell into the Milky Way and had its outer components stripped by Galactic tides. Tsuchiya et al. modeled the evolving orbit and decreasing mass of the nuclear core as the dwarf galaxy was gravitationally captured by the Milky Way. The core settled into a radial, low-inclination orbit consistent with recent observations of ω Centauri. Mizutani et al. modeled the evolving orbit of the tidal debris: the streams of stars that were stripped from the dwarf. The tidal debris is consistent with a recently observed, large relative radial velocity stream with retrograde motion.—LR

Astrophys. J. 589, L29; L89 (2003).

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