Energy X-ray image of M31. Red presents X-ray flux in the soft energy band from 0.1 to 0.4 keV, green within 0.5 to 0.9 keV, and blue within 0.9 to 2.0 keV. The main part of sources appear blue (hard) due to the galactic foreground absorption. Therefore, most of the red drawn sources are foreground stars. The ellipe sketches the D25-size of M31.