NICER Lensing

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NICER observes X-ray light from the surfaces of neutron stars. In these strong-gravity environments, light paths are distorted so that NICER can see emission from the star's far side, especially for smaller, denser stars.

With the mass of 1.5-2 suns compressed into a city-size volume, neutron stars exert a powerful gravitational force, even on the light emitted from their surfaces. For a fixed mass, the smaller the star, the more strongly light paths (pink arrows) are "bent," so that a distant observer (to the right, in this animation) can see more of the otherwise invisible far side of the star.