• Carlos R. Melo-Carneiro , Thomas E. Collett , Lindsay J. Oldham , Wolfgang Enzi , Cristina Furlanetto , Ana L. Chies-Santos andTian Li, Unveiling a 36 billion solar mass black hole at the centre of the Cosmic Horseshoe gravitational lens, https://academic.oup.com/mnras/article/541/4/2853/8213862
The little blue blob in a box at left is called the 'counter-image'. When light from behind a massive body is bent by gravity, it often forms a ring, called an 'Einstein ring', together with a counter-image.
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