Globular Clusters
Using the Hubble Space Telescope, in 1999, Buonanno et al. derived a color-magnitude diagram for Fornax 4, a globular cluster within this galaxy. Unlike the globular clusters Fornax 1, 2, 3, and 5, which have horizontal branches across a wide range of colors and include RR Lyrae variables, Fornax 4 is found to have only red in its horizontal branch. Fornax 4 is also ~3 Gyr younger than the other globular clusters. Buonanno et al. note that the color-magnitude diagram of Fornax 4 has a strong similarity to "young" galactic globular Ruprecht 106. This leads to two open questions: Why do dwarf spheroidals allow the formation of globular clusters like Fornax 4 and Terzan 7 (of Sagittarius dwarf) long after globular clusters ceased to form in the main body of the Galactic halo? Is it possible that "young" globular clusters of the outer halo like Ruprecht 106 were originally formed in now defunct dwarf spheroidals?
Read more about this topic: Fornax Dwarf
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