A black hole is a region of space from which nothing, not even light, can escape. The gas in the inner regions of the black hole become so hot that it will emit vast amounts of radiation (mainly X-rays)
This image is a simulation showing X-ray emission near a black hole.
Colors correspond to radiation intensity, black bars correspond to the polarization direction. The X-rays are emitted by gas orbiting the black hole in a thin disk, which is viewed at an inclination of 30 degrees to the normal. Intensity is greater to the left of the black hole due to boosting by special relativity. The image of the disk appears warped above the black hole due to general relativistic bending of the light rays emitted behind the black hole. The polarization is primarily horizontal far from the black hole. Close to the hole the effects of general relativistic light bending mixes the polarization, and reflection from the disk surface dilute and rotate the polarization.
GEMS, the Gravity and Extreme Magnetism Small Explorer, will detect polarized X-rays from supernova remnants, neutron stars and black holes. Polarization measurements can provide guidance. Polarized X-rays carry information about the structure of cosmic sources that is not available in any other way. GEMS can obtain significant results and prove X-ray polarization's usefulness.
