OMEGA Centauri, the largest and most massive cluster of stars in the Galaxy,
may be the victim of cosmic cannibalism. Computer simulations by astronomers in
Italy suggest it was once a dwarf galaxy, but was gobbled up by the Milky
Way.
Giovanni Carraro of the Astronomical Observatory of Padua and Cesario Lia of
the International School for Advanced Studies in Trieste simulated the evolution
of a massive gas cloud into millions of stars through successive periods of star
formation. When the resulting dwarf galaxy is captured by a nearby galaxy like
the Milky Way, the results look strikingly similar to Omega Centauri.
Last year, Korean astronomers led by Young-Wook Lee showed that Omega
Centauri contains groups of stars that formed at different times, suggesting
that the cluster was once part of a more massive system that merged with the
Milky Way (Nature, vol 402, p 55). The computer simulations by Carraro
and Lia, due to appear in Astronomy and Astrophysics, support this
idea. In particular, the simulations reproduce the abundances of heavy elements
in the cluster. “This was something that I was waiting for,” says Lee.
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If Carraro and Lia are right, Omega Centauri should be surrounded by an
extended halo of invisible dark matter, like most galaxies. Future studies of
the movements of stars in the outskirts of the globular cluster should confirm
or refute the dwarf galaxy theory.