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Double quasar QSO B0957+561

In 1979 the quasar QSO B0957+56 was the first object discovered to lie behind a gravitational lens and so was an important evidence for the correctness of Einstein's theory of relativity. The lens in the foreground is the elliptic galaxy YGKOW G1, which has a distance of about 3.5 billion light-years and isn't visible for us. Due to it, the light of the quasar is intensified and redirected in a way that makes it look double. So the light from this single quasar takes two ways to reach us, whereat the one way is 416 days further than the other. QSO B0957+56 is also known as double quasar or as twin quasar.

Constellation: Ursa Major
Distance: 8-9 billion light-years
Visual magnitude: 16.7

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    QSO B0957+561
Photo: Volkssternwarte Kempten, Christof Meier

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