November 26, 2000 Madrid, Spain – Galaxies in collision have fascinated scientists since 1877 when French astronomer Edouard Stephan discovered the first cluster that became known as Stephan’s Quintet. The name applied to a group of five galaxies (NGC7317, 7318A, 7318B, 7319 and 7320) about 270 million light-years from earth in the constellation Pegasus. A sixth galaxy, NGC7320C, shown at the bottom of the above photograph, was originally thought to be part of the colliding cluster of galaxies. When its red shift (increasing wavelength emitted by receding celestial bodies) was measured in 1961, it was moving away from earth much more slowly (800 km/second) compared to the other galaxies (6000 km/second). That puzzling and discordant measurement provoked some scientists to argue that red shift is not related to distance and that the universe was not expanding.
As the puzzle persisted, another hypothesis emerged that NGC7320 is a foreground galaxy only 35 million light years away, that red shift does measure distance and the universe is expanding. The Hubble Space Telescope now confirms with its detailed view of Stephan’s Quintet that NGC7320 is definitely closer than the more distant galaxies in collision.
Spanish scientist Mariano Moles in Madrid has studied Stephan’s Quintet for many years and says the Hubble resolution shows that the quintet is really a trio of NGC7317, 7318A and 7319 in collision. Further, Dr. Moles points out the irony that such potentially destructive galaxy collisions not only give rise to clutches of new-born stars, but “the incoming galaxies transfer energy to the group and so prevent the galaxies of the group from collapsing and merging together totally. Otherwise, one would expect the group to collapse within a few hundred million years, which is clearly not the case.”
The European Space Agency reports, “Despite being one of the most active regions in the universe, constantly under the influence of interacting galaxies, Stephan’s Quintet is still thriving and preserves a well-defined identity.”
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