Q&A: Black Holes

Q:
In the Chandra image of XTE J1118+480, are we observing the center spectral diagonal line as a line or are we seeing the line as the outside edge of a flat plane?

A:
The features in the image of XTE J1118+480 are, alas, instrumental artifacts produced by the Low Energy Transmission Grating. This instrument is an assembly of finely constructed gold gratings that are attached to the rear of the mirrors and can be swung into the path of th X-rays collected by the mirrors. In much the same way as a raindrop breaks sunlight into the colors of the rainbow, these gratings bend or diffract the reflected X-rays according to their energy. High-energy X-rays are bent less than low-energy X-rays, so they strike the detectors at different places. This is what produces the long streaks in the image. A precise measurement of the position where the X-ray hits the detector gives an exact measurement of the energy of the X-ray. The grating literally sorts the X-rays according to their energy. http://chandra.harvard.edu/about/science_instruments.html