One of the first targets for the Swift observatory's stellar survey was the giant cluster Omega Centauri, which hosts millions of stars and may be the remains of a small galaxy. Omega Centauri (also known as NGC 5139) is the largest, brightest and most massive of our galaxy's 150 or so globular star clusters. Packing some 10 million stars into a region just 150 light-years across, Omega Centauri is easily visible to the unaided eye despite lying nearly 16,000 light-years away. Unlike other star clusters, whose members all have similar age and chemical makeup, Omega Centauri displays a wide range of age and chemistry, from the ancient (12 billion years) to the relatively recent. This presence of different stellar populations suggests that Omega Centauri is not, in fact, a globular cluster, but the remnant core of a dwarf galaxy torn to shreds by the Milky Way's gravity. The false-color ultraviolet composite from images taken through Swift UVOT's ultraviolet filters reveals a treasure trove of rare stars in various stages of demise.
Credit for image on left: NASA/Swift/S. Holland (Goddard Space Flight Center), M. Siegel and E. Fonseca (Pennsylvania State University)
Credit for image on right: A. Grado/INAF-Capodimonte Observatory. Captured by the VST ESO/INAF-VST/OmegaCAM.