Europe's Quest for the Universe - Laboratoires de Recherche

46 Europe’s quest for the Universe
neglected the problems associated with the combination of the light from the
telescopes and the cost of the instrumentation. But it showed that it was not
an excessively ambitious aim to build a 16-m equivalent telescope. I made
the first proposal to do so at the ESO conference “Optical Telescopes of the
Future” held in Geneva, December 1977 5) . At this conference many interesting
ideas were presented which also helped to further crystallize our own. Of
course, the model of twenty 3.6-m telescopes was not a particularly attractive
option, but it could easily be costed. A more ambitious project with larger
unit telescopes was called for, but needed more analysis.
At the time I listed just five illustrative examples of what such a
telescope would do. They were the following:
1. Abundances of elements in globular cluster stars. Composition variations
were believed to be due to differences in the elemental abundances of the
gaseous medium from which such stars formed, but since only evolved stars
could be observed effects of stellar evolution could also play a role. But
adequate analysis of unevolved stars was hardly possible because they
were too faint for 4-m class telescopes. Actually the VLT has been used
extensively to study the abundances of cluster and halo stars.
2. The motion of globular clusters in other galaxies informs us about their
masses and about their “dark matter” content.
3. Cosmological studies involving faint galaxies and quasars would be of
much importance. While the faintest objects might best be detected with
the Hubble Space Telescope, more detailed spectroscopy of somewhat
brighter objects would be the domain of the 16-m telescope. This complementarity
has been very much in evidence with the VLT.
4. Correlative optical studies of radio and X-ray sources. In fact, extremely
faint counterparts to X-ray sources have been found at the limit of what
the VLT can observe.
5. High time resolution photometry of X-ray sources. Today one would have
replaced this by observations of remote supernovae to determine the
structure of the Universe.
Of course, many other topics could have been listed, in particular also
in the infrared.
To me it seemed highly premature to go in one step to a 16-m telescope.
ESO had constructed a moderately satisfactory 3.6-m. The USSR 6-m
telescope was the largest in the world. It was a heavy monster. Just scaling
up these telescopes to 16-m was not going to work. The step to 16 m was too
large. If something would go wrong, the loss would be total. On the other
hand, the optical combination of a large number of small telescopes would
lead to important light losses, which could defeat the aim of efficient photon
collection. And if all of these would be individually instrumented, the cost
of the instruments might become a large part of the total. While such an array
might yield high angular resolution on bright objects when used in an interferometric
mode, for the imaging of very faint objects it would be far from