A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. The size of the X-ray image is smaller because the higher energy X-ray emitting electrons radiate away their energy more quickly than the lower energy optically emitting electrons as they move.
Credits for X-ray Image: NASA/CXC/ASU/J. Hester et al.
Credits for Optical Image: NASA/HST/ASU/J. Hester et al.