A handful of high-speed quasars.

A handful of high-speed quasars 

Quasars have repeatedly provided surprises for astrophysicists. Through the telescope, quasars look like stars, but from their frist discovery 25 years ago it was clear that they are not stars: They radiate energy at rates equivalent to whole galaxies. Detailed inspection, using the technique known as radio interferometry, shows that quasars tend to consist of a number of blobs, lobes and jets of matter apparently shot out of some central source. In a few cases, soem of the blobs seem to be moving faster than light. These "superluminals" have occasioned a lot of discussion, but until recently they appeared to be rare.

Now, a single series of observations doubles their number from seven to 14 and may soon triple it. Six others studied in the survey are likely to prove "superluminal" after another year's observation of their movements.

this sudden population increase means that "superluminals" can no longer be regarded as rarities. They become a class of astrophysical objects that needs a consistent and believable theoretical explanation.

"Superluminal" is in quotes because reputable astrophysicists overwhelmingly do not believe that anything is really moving faster than light. The appearance of superluminal motion is held to be an optical illusion, but the illusion imposes serious difficulties on attempts at an explanation.

Astronomers determine the motions by combining and comparing signals received from a particular quasar at widely separated receiving stations. From the correlations and differences among the signals, they can deduce details of the quasar's structure too fine for a single telescope to make out. In this case, radiotelescopes distributed from California to central Europe were used. Led by Anthony Readhead, director of Caltech's Owens Valley Radio Observatory at Big Pine, Calif., the group includes astronomers from the Max Planck Institute for Radio Astronomy in Bonn, West Germany, and fron the Naval Research Laboratory in Washington, D.C. They are submitting reports to ASTROPHYSICAL JOURNAL, NATIRE and ASTRONOMY AND ASTROPHYSICS.

Combining such widely spaced receptions, the astronomers draw charts of the detailed structure of the quasar. When they return and observe it again after a certain lapse of time, they find that some of the blobs have moved. In this way, apparent velocities up to seven or eight times that of light have been calculated.

According to the theory of special relativity, no material object can go faster than light, but the same theory yields a way of explaining these motions as lamost but not quite at the speed of light . Suppose these "superluminal" blobs are coming toward us, or nearly so. In that case, special relativity provides for a difference in the perception of time: The time in which terrestrial observers see the motion taking place is less than the time perceived by a hypothetical observer riding on the blob, and so the motion appears faster to the terrestrial observer than it does in the blob's frame of reference.

In that way, nothing is going faster than light in itss own frame of reference, and so the cosmic speed limit is not violated. Nevertheless, this means that some of the observed blobs are going at rates of up to 99 percent of the speed of light in their own reference frames.

If this explanation holds, all the "superluminals" we see must be coming more or less straight at us; by definition it doesn't work for motions at right angles to our line of sight. If we see a large number of "superluminals" pointed at us, then, by the usual randomness of nature, there must be even more than we don't seem to see pointing in various directions -- unless the earth is a specially privileged location, an idea that astronomers don't like.

As Kenneth Johnston of the Naval Research Lab points out, there is an explanation why we should preferentially see the ones pointed toward us: "The theory of relativity indicates that any radiation from an object that is moving at nearly the speed of light is strongly beamed in the direction of motion," he says. "Thus objects moving toward us will appear unusually bright, and therefore easy to see, while objects moving at large angles to the line of sight will be relatively faint and difficult to see."

Even so, if the number of "superluminals" continues to climb, this relativistic-illusion explanation may become strained: It will be more and more difficult to believe that so many of the most energetic and violent objects in the universe point themselves right at us. Astronomers may be fooling themselves to think that all these blobs are moving in the line of sight.