This cool space wallpaper shows an optical color image of galaxies overlaid with X-ray data (magenta) from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR). NuSTAR's serendipitous discovery in this field (left magenta blob) lies to the left of a galaxy, called IC751, at which the telescope originally intended to look. Both magenta blobs show X-rays from massive black holes buried at the hearts of galaxies. This image was released Sept. 5, 2013.
(Image: © NASA/JPL-Caltech)