... The answer is usually the most exotic and energetic of astrophysical environments, like active galaxies powered by supermassive black holes, or incredibly dense pulsars, the spinning remnants of exploded stars. ... The M81 Galaxy Group Through the Integrated Flux Nebula . ... Large galaxies and faint nebulae highlight this deep image of the M81 Group of galaxies. ... The dark band of dust that obscures the mid-section of the Sombrero Galaxy in optical light actually glows brightly in infrared light....