ARG%SU-AI@sri-unix.UUCP (12/28/83)
From: Ron Goldman <ARG@SU-AI>
n068 1715 26 Dec 83
BC-SPEED 2takes
(ScienceTimes)
By WALTER SULLIVAN
c.1983 N.Y. Times News Service
NEW YORK - Perhaps the most fundamental theoretical underpinning of
modern physics is the conviction that nothing moves faster than light.
But now observers have reported sighting objects far out in space
that appear to be moving at more than 15 times the speed of light.
One of those objects, as reported recently in the journal Nature,
appears to be picking up speed.
Various explanations have been proposed. All leave some basic
questions unanswered, though physicists remain unshaken in their
belief that the speed limit holds throughout the universe.
One theory relates to the so-called ''motion of effects,'' such as
the moving point of closure on a closing pair of shears, or the
moving spot of light cast by a flashlight on a distant wall. The
speed limit of light does not apply to the motion of effects, as it
does to the motion of material things.
Such an effect has been seen by astronomers on the Earth observing
the illumination of a large, spherical shell of gas by an exploding
star in its center. Light from the explosion reaches all parts of the
shell at the same time, but the part nearest the Earth is first seen
to flare up, since light from that region has the least distance to
travel to the Earth. As this area fades, light from the surrounding
regions begins to arrive at the Earth, creating the appearance of an
illuminated ring. The ring may appear to expand faster than the speed
of light until the light from the outer edge arrives.
But radio astronomy has revealed far more distant objects that also
appear to be traveling faster than light. These so-called
superluminal objects do not fit readily into the motion-of-effects
theory. The favored explanation is that they have been ejected at
almost, but not quite, the speed of light and are coming almost, but
not quite, straight at the Earth.
According to one calculation, they must be aimed no more than eight
degrees away from a line pointing directly toward the Earth. But rest
assured, these objects are so far away that, even if they were to
make eight-degree midcourse corrections, they would not hit the Earth
for a billion years or more.
If superluminals are actually traveling at such high speed and
almost straight toward the Earth, their apparent speed should be
enormously exaggerated.
To see how this could happen, suppose a Moon-gazer on the Earth sees
the flash of a rocket being fired from the darkened portion of a new
Moon. Then, a fraction of a second later, the gazer sees a point of
light, the rocket itself, far to one side of the Moon. It would
appear to have traveled there almost instantaneously.
This could be explained if the rocket was fired at almost the speed
of light, 186,000 miles per second, and aimed at a point close to the
Earth. To an observer who is unaware that the rocket is heading
toward the Earth at extremely high speed, it would appear from the
Earth to have moved off to the side of the Moon almost instantly.
The actual flight of the rocket, at close to the speed of light,
would be only a short distance behind the light waves from the flash
of its liftoff from the Moon. Thus the light carrying the image of
the rocket long after it was launched would arrive almost at the same
instant as that from its launching. The implication is an incredibly
fast traveling speed. But the actual speed is slower. Clearly, you
cannot see the rocket's liftoff the moment it occurs, since the light
from its blast must travel 240,000 miles to the Earth. So, the time
elapsing between liftoff and the moment you see the rocket far out in
space is greater than it seems. Therefore, the actual speed is less.
At least seven superluminal objects or chains of objects have been
charted by networks of radio telescopes in this country and Europe.
All the superluminal objects appear to be embedded in jets radiating
from quasars. Quasars are celestial objects that emit immense
quantities of light waves or radio waves, which are longer waves in
the spectrum. Some of the brightest quasars, or radio galaxies, eject
jets in opposite directions, but the superluminals seem to be coming
from quasars with one jet only. Astronomers suspect one-jet quasars
really have two jets, but one of them is aimed almost directly at the
Earth. The other, going in the opposite direction, would be moving
away from us so close to the speed of light that it could not be seen.
For some reason, these jets do not spread out like the jet from a
hose, but instead remain narrow over distances of thousands of
light-years. A problem no less deep is what generates the jets in the
first place.
It is widely suspected that the energy source, or ''engine,'' in the
heart of the quasar is a rapidly rotating object of enormous density,
such as a black hole, in which matter is so concentrated that nothing
can escape it. The jets are thought to be directed along the spin
axis of this object. The single jets tend to curve, and the
superluminal objects seem to be traveling along the same curved paths.
As reported in Nature, however, a fourth object has now appeared in
a procession of three previously tracked superluminal features flying
out from the quasar 3C-345. This, unlike the others, seems to be
moving in a straight line. The manner in which such objects are
ejected has been mapped with increasing detail as technology
improves. The circular region of intense radio emission, defining the
quasar, develops a bulge, which then pinches off as a separate
structure and moves away.
The observing method, known as long baseline interferometry,
requires several stations to observe the target area simultaneously,
using atomic clocks to keep a highly precise record of arrival times
of the radio waves. The recordings can then be meshed to produce a
map of the source region. The more widely separated the antennas, the
greater the detail that can be detected.
The apparently straight path of the newly found superluminal object
does not lead back into the core of the parent quasar. If its source
were indeed the quasar core, it must have flown a sharp curve before
it was observed.
According to Dr. Marshall H. Cohen of the California Institute of
Technology, who has played a leading role in the observations, the
paths flown by the first three superluminals may not be curved as
much as they appear. If they are coming almost straight at the Earth,
the curvature, which may be a response to some form of pressure along
the path of the jet, could appear exaggerated.
The apparent velocity of the fast-moving components depends on the
assumption that they are extremely far from the Earth. That
assumption, in turn, is based on the shifting of quasar light waves
toward the red end of the spectrum, taken by most astronomers as
evidence that they are receding at large fractions of the speed of
light and therefore must be very far away in the expanding universe.
Cohen's co-authors in one of the two reports in the Nature article
were J.A. Biretta and S.C. Unwin of Cal Tech, and I.I.K. Pauliny-Toth
of the Max Planck Institute for Radio Astronomy in Bonn. The other
paper, by R.L. Moore and A.C.S. Readhead of Cal Tech, and L. Baath of
Onsala, Sweden, describes an apparent acceleration of the newest
component from 6.8 to 11.2 times the speed of light.
In a recent telephone interview, however, Cohen pointed out that an
appearance of acceleration could be produced, without any actual
increase in velocity, if the source's spiraling trajectory increased
its motion across the line of sight from the earth.
nyt-12-26-83 2010est
***************REM%MIT-MC@sri-unix.UUCP (12/30/83)
From: Robert Elton Maas <REM @ MIT-MC> If most of the energy emitted by a jet is sent in essentially the "forward" direction, that is nearly the same direction as the jet itself is moving, which is reasonable for some methods of emitting energy, then jets not aimed nearly directly at us wouldn't emit energy we could see, thus a high percentage of jets would show the superluminal effect compared to if we sampled all directions of jets fairly. Thus I'm not much surprised that we've observed many of these things, and I accept that they are all sub-cee-speed objects in reality until proven otherwise. One test would be blueshift in the jet compared to the quasar itself. If the jets are observed only at radio wavelengths, spectral lines might be difficult to identify. Anybody have info about blueshift or not blueshift of apparent-superluminal quasar jets?