A few lucky stars in spiral galaxies belong to beautiful
clusters of young stars, but most roam the galaxy alone or with
just a partner or two. Now, as astronomers will report in
theMonthly Notices of the Royal Astronomical Society, a star's
chances of being born in a cluster depend on how close it is tothe
galaxy's center. The researchers mapped thousands of star clusters
in the attractive barred spiral galaxy M83 (shown), 15 million
light-years from Earth, finding that the percentage of young stars
in clusters declines from the urban core to the suburbs: Four
thousand light-years from M83's center, 19% of young stars belong
to clusters, whereas 13,000 light-years out, just 7% do. This trend
may arise because starmaking molecular gas abounds in the inner
regions of a spiral galaxy's disk, increasing the gas pressure and
the chances of cluster formation. M83 is the first galaxy in which
astronomers have discovered this trend, but other spirals likely
follow the same pattern, tooincluding the Milky Way, the one galaxy
we can't see from the outside.
