Arp's Phantom Jet
Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.
During the “Great Debate” of 1920 astronomers Herber Curtis and Harlow Shapley had a famous debate on the nature of “spiral nebulae”. Curtis argued they were “island universes” or what we would today call a galaxy. Shapley was of the opinion that they were spiral structures within our own galaxy. One of the evidences Shapley put forth was that another astronomer, Adriaan vanMaanen, had reported detecting rotation of these objects over a period of years leading to an overall rotation rate of ~105 years. If these spiral nebulae were truly as far (and thus, as large) as Curtis suggested this would mean they would be rotating well beyond the speed of light at their outer edges.
It was later determined vanMaanen's rotation was a case of wishful thinking when Hubble eventually determined the true distance to the Andromeda galaxy. From then on, it was well established that galaxies are so large, their motions will not be observed in human lifetimes. Aside from local flare ups of supernovae and other such events, galaxies should be relatively static. Yet in just over 40 years, a distinct, large-scale feature in the galaxy NGC 3303 seems to have disappeared entirely.(...)
Read the rest of Arp's Phantom Jet (457 words)
