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showing that the focusing of light from 
a distant galaxy by a closer one would 
intensify the former’s brightness by 
a factor of as much as 100. He pointed 
out that if astronomers could find such 
gravitational images, they would be 
able to explore the universe to much 
greater distances than otherwise pos- 
sible, since very distant galaxies 
(which ordinarily would be too faint 
to be seen) would be intensified to 
the point of observability. 
Despite Zwicky’s “farsighted” sug- 
gestion, no clear case of gravitational 
imaging of one galaxy by another has 
ever turned up. Astronomers have, 
however, found another way to explore 
the universe beyond the distance of 
the faintest detectable galaxies: they 
discovered quasars. As I mentioned 
earlier, quasars are much brighter 
than galaxies and hence are detectable 
at greater distances. In fact, shortly 
after the first quasars were found in 
1963, it was suggested that they were 
all gravitationally focused images. 
Specifically, it was proposed that qua- 
sars are not a unique type of cosmic 
object but rather gravitational images 
of the central cores of very distant 
galaxies. The suggestion did not pan 
out and, in fact, was never taken very 
seriously by most astronomers. 
When Walsh, Carswell, and Wey- 
mann reported that they had found 
a pair of gravitational images, many 
astronomers remained skeptical. 
“Where is the lens?” they wanted to 
know. Existing photographs such as 
those from the Palomar Sky Survey 
did not show a foreground galaxy be- 
tween A and B, nor did photographs 
taken specifically for this purpose in 
Arizona after the March discovery. 
The Walsh team expected that the 
lens galaxy would be midway between 
A and B, as seen from the earth, be- 
cause the two quasar images are of 
nearly equal brightness. 
It was not until November 1979 
that astronomers at the California In- 
stitute of Technology and at the Uni- 
versity of Hawaii succeeded in ob- 
taining telescopic photographs good 
enough to reveal the missing lens. Sen- 
sitive electronic cameras made this 
possible. Surprisingly, the lens is not 
midway between A and B, but rather 
just slightly north of the southern qua- 
sar image, B. The lens is a very large 
elliptical galaxy, a member of a cluster 
of galaxies located less than halfway 
from the earth to the real quasar. As 
the light from the quasar travels to- 
ward the earth, it is deflected and 
28 
