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An image of the Milky Way warped around a small black circle at the centre of the image.
An artist’s impression of a black hole, where the black hole’s intense gravitational field distorts the space around it. This warps images of background light, lined up almost directly behind it, into distinct circular rings. This gravitational "lensing" effect offers an observation method to infer the presence of black holes and measure their mass, based on how significant the light bending is. The Hubble Space Telescope targets distant galaxies whose light passes very close to the centers of intervening foreground galaxies, which are expected to host supermassive black-holes over a billion times the mass of the sun.
ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org), N. Bartmann