determined by the density of the surrounding material it encounters. This type of x-ray data provides a wealth of information about the nature and distribution of the interstellar medium around the original supernova. Bright knots and filaments show regions of higher density, whereas the gradual lessening of intensity (to the lower right) is characteristic of less material. Here the spherical blast travels without encountering much material to heat, so few x-rays are produced. Spectroscopic data of the same region provides information on the temperature and composi- tion of the hot gas.
