@nasa : As seen on #Cosmos: The Gravitational Lens Imagine a bright object such as a star, a galaxy, or a quasar, that is very far away from Earth (say...10 billion light years). For our discussion, let us imagine we have a quasar. If there is nothing between it and us, we see one image of the quasar. Yet, if a massive galaxy (or cluster of galaxies) is blocking the direct view to the quasar, the light will be bent by the gravitational field around the galaxy. This is called "gravitational lensing," since the gravity of the intervening galaxy acts like a lens to redirect the light rays. But rather than creating a single image of the quasar, the gravitational lens creates multiple images. We follow the light rays from the Earth to the apparent locations of the quasar. If the galaxy were perfectly symmetric with respect to the line between the quasar and the Earth, then we would see a ring of quasars! The Hubble Space Telescope has peered nearly 5 billion light-years away to resolve intricate details in the galaxy cluster Abell 370, seen here. Abell 370 is one of the very first galaxy clusters where astronomers observed the phenomenon of gravitational lensing, where the warping of space by the cluster's gravitational field distorts the light from galaxies lying far behind it. This is manifested as arcs and streaks in the picture, which are the stretched images of background galaxies. Image credit: NASA, ESA, the Hubble SM4 ERO Team, and ST-ECF #space #nasa #universe #hubble
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