VLBI observations

From the centers of quasars calculated to have velocities 10 times greater than that of light—the Einsteinian constant of the universe—astronomers are finding explanations of Doppler effect red shifts of emission. Very long baseline interferometry (VLBI) arrays have been used to examine the cores of seven known radio sources in space that are characterized by superluminal velocities, and a significant amount of knowledge has been gained about red‐shift phenomena of plasma sources. Milliarcsecond resolution of VLBI techniques allows observers to examine in detail central structures of radio sources. According to a discussion of observers at the recent superluminal workshop held at the Jodrell Bank Observatory, U.K., February 1983, “The last six years have brought a great increase in reliability of results, particularly because of the use of VLBI arrays…” (Nature, April 28, 1983). This reliability has resulted in a compilation of properties of radio‐source core structures. The steep frequency‐shifted radio spectrum of a superluminal structure is apparently caused by rapidly extending plasma jets. The discussion provides the following explanation of a relativistic jet: “…a relativistically moving stream of plasma emanating from the core…[which]… is identified with the base of the jet. … The ‘moving’ components are shocks or plasmons moving down the jet, which point toward the observers in the case of superluminal sources” (Nature, April 28, 1983). The idea is that illusions of Doppler effect red shifts can be produced by high‐energy physical phenomena other than simple velocity effects. Even in the case of a source moving away from an observer with a relative velocity less than the speed of light, an illusion of superluminal velocity results because the angle of view is small (“because the observer's view of the early part of the motion is delayed with respect to the later parts, and hence the apparent duration of the motion is shortened” (Nature, April 28, 1983)).