The globular cluster NGC 6397

This ESA/NASA/ESA Hubble Space Telescope Wide Field Planetary Camera 2 image shows the globular cluster NGC 6397 in the constellation Ara (the Altar). It is composed of six exposures through different filters: violet/indigo (Strvmgren u, 345 nm, 15080 seconds), blue (B, 418 nm, 8580 seconds), dark green (V, 515 nm, 978 seconds), light green (H-alpha, 656 nm, 24180 seconds), red-orange (R, 678 nm, 1538 seconds), and red (I, 839 nm, 978 seconds). The cluster is home to a highly unusual system consisting of a fast spinning pulsar and a bloated red companion star.