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Zwicky (1953,56)

Fritz Zwicky was the first to start systematically photographing peculiar galaxies using his 18 inch Schmidt camera at Palomar. Using these images, he quickly concluded that many of the narrow filaments that he observed must be due to tides stemming from gravitational interactions. In a 1953 issue of Physics Today, he described these filaments as tides and countertides and furthermore, correctly deduced that the narrowest of them must be sheets of matter seen edge on; furthermore, he emphasized that much of the visible matter in the bridges and tails must consist of stars. Shown below is one of his sketches - "the possible formation of an intergalactic bridge between two galaxies passing each other".

In the sketch, Zwicky considers the possible bridge formation between two interacting galaxies; the resulting configuration closely resembles Arp 96. Note that the lower galaxy in instances (a) and (b) becomes the upper galaxy in instances (c) and (d).

Chris Power
Thu Sep 16 20:11:54 BST 1999