M33, Einstein
M33 is a nearby example of a spiral galaxy. It is only slightly inclined to our line of sight such that we can see both structure in the spiral arms, and the central bulge. Observations of galaxies like these can help us determine the structure of our own Galaxy, the Milky Way.

This image shows M33 in X-rays as observed by the Einstein Observatory, a telescope which orbited the Earth between 1978 and 1981. The background greyscale image is an optical photograph while the contours are the X-ray data. This shows that most of the high energy photons are coming from the centre of the galaxy where astronomers think that a black hole exists.

Image credit: Einstein Observatory