Far ultraviolet (FUV) emission is observed in the central regions of cool-core clusters with the Hubble Space Telescope (HST). It is traced out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be distributed in clumps and filaments, as shown in Figure 1. The FUV emission matches the global structure of the ionized gas nebulae. If produced by stars, this emission can account for the ionization but not the temperature of the gas (Voit & Donahue 1997; Oonk et al. in preparation).
