Why some stars are born alone

ESO

Why some stars are born alone

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 the Monthly Notices of the Royal Astronomical Society, a star's chances of being born in a cluster depend on how close it is to the 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, too—including the Milky Way, the one galaxy we can't see from the outside.