images, primary and secondary
  • In relativistic cosmology, the primary image is the main image of a star orbiting a black hole. Because of gravitational attraction pulling the star’s light towards the hole, this image traces out a complex path during the course of a single orbit of the star around the black hole. The secondary image, however, traces out a yet more complex pattern in the sky. It is made up of light which has made a single orbit of the black hole before escaping to be observed, so that the geometry governing the route taken by the light on the way to the observer is complex. There are also tertiary and higher images, of even more complexity. In these cases the light has had a more lengthy entanglement in the gravitational field of the hole before escaping to the observer. These higher order images contain steadily less and less energy, making them ever less likely to be observed. They would exhibit a single point of light moving according to the inclination of the black hole’s rotation to the Earth and other factors.

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