January 1, 2004 | David F. Coppedge

Globular Cluster Origins: Where Do We Go From Here?

The simple explanation of globular clusters as bundles of ancient stars seems to be in a state of crisis, though the authors of a paper in the Jan. 1 issue of Nature1 try to keep a stiff upper lip.  They begin, “Nearly a century after the true nature of galaxies as distant ‘island universes’ was established, their origin and evolution remain great unsolved problems of modern astrophysics.
    For one thing, how could globulars survive all the tumult?  “Recent advances in our understanding of the globular cluster systems of the Milky Way and other galaxies point to a complex picture of galaxy genesis driven by cannibalism, collisions, bursts of star formation and other tumultuous events.”  It appears now that they cannot assume that the high metallicity (content of atoms heavier than helium) in cluster stars is an indication of old age.
    Current thinking is a debate between competing models dealing with uncooperative observations.  After showing strengths and weaknesses of contenders, they ask, “Where do we go from here?”  Much work remains to be done, they admit.  Although they offer some promising areas of research, it may be that the origin and evolution of each galaxy may be unique:

Detailed spectroscopic and photometric observations of the most massive galaxies in dense environments show that their globular cluster populations are generally old and coeval to within a couple of billion years.  But the age distribution of globular clusters remains an open question, as several recent studies have found a wider spread of globular cluster ages in some galaxies, including the presence of some intermediate-age metal-rich clusters.  The findings to date suggest a complex picture of globular cluster formation in galaxies, with the formation histories of no two galaxies being exactly alike.

Not to end on a minor chord, they triumphantly promise that the quest for understanding galactic evolution marches on:

These are exciting times in the study of extragalactic globular cluster systems.  Disentangling the myriad processes that may have contributed to the formation of nearby galaxies is a formidable challenge, but the potential reward is spectacular: a glimpse into the evolutionary histories of individual galaxies.

See also the Oct. 5 entry on globular clusters.

Michael J. West et al., “Reconstructing galaxy histories from globular clusters” (review article), Nature 427, 31 – 35 (01 January 2004); doi:10.1038/nature02235.

We don’t know where we are, we don’t know how we got here, the territory is far more complex and formidable than we thought, and we don’t know where to go from here, but at least we can imagine how nice it would be to find our way some day.  How much do you trust this bunch?

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Categories: Astronomy, Cosmology

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