Interview with Massimo Tarenghi

((VLT-program director and head of ESO- European Southern Observatory - telescope division)) about the perspectives of observational astronomy

Georg Wolschin: How do the new telescopes and instruments of observational astronomy fit into the various regions of the electromagnetic spectrum?

Massimo Tarenghi: At ESO we are convinced that the future in astronomy will be to push the millimeter wavelength. This is a domain in which we want to see deep in the space and study thermal emissions. So ALMA (Atacama Large Millimeter Array) is for us the project which has highest importance. We will cover an area of production of energy in the universe that so far has not been investigated sufficiently, and discover the physical mechanisms at the beginning of galaxy formation. Next we want to build really big optical telescopes of the 100-meter-class and learn from the experience gained so far when manufacturing big telescopes, and - this is very important - take full advantage of adaptive optics: the possibility to remove the turbulence of the atmosphere. Therefore it makes sense to have this machine. Adaptive optics is at the beginning, but we know how to tackle the thing.

GW: In the X-ray region, the new satellits Chandra and XMM are of particular interest.

T: These recently launched spacecraft give us new physical information at high energies and are complementary to the other machines that we are building. The possibility to combine the X-ray light of different telescopes into one image is going to be the guide for future programs in X-ray astronomy.

GW: Point source investigations and surveys will not only be carried out using X-rays, but simultaneously in the other spectral regions?

T: Absolutely. In surveys we like to cover a large part of the sky in the X-ray, optical and infrared region. That has been initiated with the Hubble space telescope, and now we are also doing it from the ground: to take pieces of the sky and expose for hours and hours is the way to really accumulate large numbers of information. And then, when you have this kind of survey, you can use the big machines and pick up individual objects. This could be a galaxy at the beginning of its formation or other objects at really high redshift or - and this is the beauty of big telescopes - you can observe nearby, but intrinsically faint objects that escaped the past telescopes such as planets around stars. The big dream that we have in front of us with interferometry and 100-meter-telescopes is not only to detect the existence of these planets - we know already that they exist - but also the dynamics. And what I think is fundamental: to be able to receive from them enough photons distinguished from the star in order to analyse the spectrum.

GW: As long as the 100-meter-telescope does not exist: What is currently the most promising method for the direct detection of extrasolar planets?

T: That is clearly interferometry. The VLTI ((Interferometer at the Very Large Telescope in Chile, 4 coupled eigth-meter telescopes)) will be a machine that is able to do this kind of thing. Of course, we will then need the 100-meter-telescope for a detailed spectral analysis.

GW: In space, there will also be a successor to the Hubble space telescope: the Next Generation Space Telescope, NGST. Comparing that to the VLT ((Very Large Telescope in the Atacama desert, Chile)), what are its advantages and disadvantages? Certainly, interferometry will not be possible there.

T: This will be an eight-meter telescope in the space, but a single one - to be launched around 2010. It will be dominant in the infrared, but the VLT remains important for the optical domain. I think when we will be able - and this is a matter of a couple of years - to have adaptive optics on the VLT and to remove the effect of the atmosphere, we are comparable with the NGST. As a matter of fact, NASA is designing this machine primarily for the infrared, because there is no reason to compete, but rather to cooperate.

GW: When do you plan to implement a terrestrial 100-meter-telescope?

T: According to our ideas we could have "First Light" around 2017. That is a long time in front of us, but also with the VLT it took about 20 years from the first idea to completion. And now, seeing backward, that time seems so short.

GW: What is going to be the material for the 100-meter-mirror?

T: We are exploring different materials. We are trying right now conventional materials, for example zerodur. Such a mirror would be segmented. Our concept is to build about 2000 segments. The problem is to be able to produce about two such mirrors per week, but this can be handled with current technology. The surface accuracy of 7 nanometers that has been reached at the VLT is sufficient for the future.

GW: Will this be a pure ESO-project?

T: It cannot be a pure ESO-project. When we work in this kind of dimension we must cooperate with many factors. One of the reasons why we created the Club-100 is to foster the cooperation with other partners. I am sure it will be a world-wide effort. A few years ago I created the 8-meter club with american and japanese colleagues, and we have seen the benefit of this kind of exchange of information. Here we are talking about not only exchange of information, but putting together the forces in order to achieve a big, big goal.

GW: One is also interested in the detection of gravitational waves, which are generated when cosmic masses are accelerated such as in a supernova-explosion. There will be terrestrial projects like VIRGO and LIGO, and there will be at least one interferometer in space, LISA. What is the more promising approach?

T: As in case of ground-based and space optical astronomy, there is no way one field can do alone. You need both, because on the ground you can experiment with new technology - in space, you push it. For gravitational waves, the new projects in space and on the ground are showing that we are entering a domain of sensitivity of the detectors where our physics theory can be tested even if gravitational waves are not yet detected, and therefore we enter in a mature stage. It is very interesting to see that many of the technologies that are used in gravitational wave detectors are very similar to the ones used in optical interferometry. After all, we also have to measure distance, and keep distance. Because the technology is very similar, we have a strong exchange of information, although the goal is different. I really hope that soon we will see gravitational waves, and through simultaneous observations of electromagnetic radiation, also their source - such as a supernova-explosion. As astronomer, I will be fascinated, and the theory and the physics will be revolutionized by this detection.

Figure: NGST, or ALMA, or 100-meter-telescope.

A translated and (through the editors) abbreviated version of this interview has appeared in Spektrum der Wissenschaft 6 (2000)

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