The background picture was taken with an ordinary optical telescope on Earth. The lines drawn on top, known as countour lines, are the X-ray image, taken by the Einstein Observatory, a satellite which orbited the Earth between 1978 and 1981 and took the first X-ray images from space. You can think of the lines just like those on an ordinary contour map you might use when you go hiking. Instead of marking points of the same height, these contours mark points of the same brightness.
The dust lane is now invisible because X-rays are unaffected by dust, so they pass straight through.
Image credit: Einstein Observatory