The Messenger
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The Messenger No. 121 – September 2005 Science with Extremely Large Telescopes Figure 1: Concepts for 50–100-m ELTs. Left: the OWL (Over Whelmingly Large) Telescope, a design for a 100-m-class telescope being developed by ESO (Gilmozzi 2004, Dierickx et al. 2004). Right: The Euro-50 concept (Andersen et al., 2003, 2004). Isobel Hook (University of Oxford) In the past half-century a new generation scope (TMT). In Europe the focus is on and the OPTICON ELT Science of telescopes and instruments allowed even larger telescopes – preliminary stud- Working Group remarkable new discoveries: quasars, ies indicate that the technology to achieve http://www.astro-opticon.org/ masers, black holes, gravitational arcs, a quantum leap in telescope size is fea- networking/elt.html extra-solar planets, gamma ray-bursts, sible, and a detailed design study is now the cosmic microwave background, dark under way in Europe (led by ESO) to matter and dark energy have all been develop the technology needed to build a Astronomers around Europe are gearing discovered through the development of a 50–100-m telescope (see Figure 1). up for the next generation of ground- succession of ever larger and more based telescopes to follow on from the sophisticated telescopes. This progress A larger telescope is beneficial for two success of the VLT and other 6–10-m poses new, and more fundamental, main reasons – firstly, a larger collecting telescopes. All aspects of astronomy questions, the answers to some of which area (proportional to the square of the will be dramatically advanced by the will perhaps unite astrophysics with diameter) allows fainter and more distant enormous improvements attainable in elementary particle physics in a new ap- objects to be observed. Secondly, the collecting area and angular resolution: proach to the nature of matter, while resolution achievable improves in propor- major new classes of astronomical ob- others may give us insights as to the exis- tion to diameter of the telescope, pro- jects will become accessible to obser- tence (or otherwise) of other life-sup- vided that the telescope is equipped with vation for the first time. In July of this porting planets in our Galaxy. As the cur- an adaptive optics system that corrects year a book1 was produced by a group rent generation of telescopes continues for the blurring effects of the Earth’s at- of European astronomers, which de- to probe the universe and challenge our mosphere. Thus a 50-m telescope work- scribes the science achievable with a understanding, the time has come to take ing at its diffraction limit could in theory telescope of diameter 50–100 m. Here the next step. produce images over five times sharper we present some highlights from this than the best images from today’s 6–10-m science case, ranging from direct ob- Several projects are under way around telescopes. These two effects together servations of Earth-like planets outside the world to design and construct have a profound effect on the scientific our own Solar System to the most dis- the next generation of ground-based, Ex- observations that can be made – from the tant objects in the Universe. tremely Large Telescopes (ELTs), which ability to resolve faint planets around will provide astronomers with the ability to other stars, to studying the most distant 1 Hook, I. M. (Ed.), 2005, “The Science Case for the address the next generation of scientific object in the Universe. European Extremely Large Telescope: The next step questions. Initial studies in the United in mankind’s quest for the Universe”. Printed copies States and Canada are concentrating on Some examples are given below of the and CDs are available on request from Suzanne potential designs in the 20–30-m range, potential scientific breakthroughs achiev- Howard ([email protected]). PDF files can be downloaded from http://www.astro-opticon.org/ such as the proposed Giant Magellan able with the vast improvement in sen- networking/elt.html Telescope (GMT) and Thirty Meter Tele- sitivity and precision allowed by the next 2 The Messenger 121 – September 2005 step in technological capabilities, focus- Table 1: Highlight science cases for a 50–100-m Extremely Large Telescope. ing on the science case for a 50–100-m telescope, which is being developed in Are there Terrestrial planets orbiting Are we alone? Direct detection of earth-like planets in extra-solar Europe. Additionally, as we have seen other stars? systems and a first search for bio-markers (e.g water and oxygen) in the past, each new generation of facili- becomes feasible. ties has advanced science by discover- How typical is our Solar System? What Direct study of planetary systems during their formation from proto- are the planetary environments around planetary disks will become possible for many nearby very young ing the new and unexpected. Therefore it other stars? stars. In mature planetary systems, detailed spectroscopic analysis is likely that the major scientific impact of Jupiter-like planets, determining their composition and atmos- of these new telescopes will be discover- pheres, will be feasible. Imaging of the outer planets and asteroids in ies beyond those we can predict today. our Solar System will complement space missions. When did galaxies form their stars? When and where did the stars now in galaxies form? Precision stud- ies of individual stars determine ages and the distribution of the chemical elements, keys to understanding galaxy assembly and evo- Are we alone? lution. Extension of such analyses to a representative section of Planets beyond our Solar System the Universe is the next great challenge in understanding galaxies. How many supermassive black holes Do all galaxies host monsters? Why are supermassive black holes in In 1995 the first planet around a normal exist? the nuclei of galaxies apparently related to the whole galaxy? When and how do they form and evolve? Extreme resolution and sensitivity star other than the Sun was detected, are needed to extend studies to normal and low-mass galaxies to by the Swiss astronomers Mayor and address these key puzzles. Queloz, using a small French telescope When and where did the stars and the Can we meet the grand challenge, to trace star formation back to with sophisticated instrumentation. The chemical elements form? the very first star ever formed? By discovering and analysing distant rate of announcement of new discov- galaxies, gas clouds, and supernovae, the history of star formation, and the creation history of the chemical elements can be quantified. eries of extra-solar planets currently ex- What were the first objects? Were stars the first objects to form? Were the first stars the source ceeds several tens per year, with dis- of the ultraviolet photons which re-ionised the Universe some coveries dominated by indirect methods: 200 million years after the Big Bang, and made it transparent? These either the motion of the parent star in- objects may be visible through their supernovae, or their ionisa- duced by the gravitational pull of the plan- tion zones. et, or the light-loss resulting as the planet How many types of matter exist? What Most matter is transparent, and is detectable only through its gra- is dark matter? Where is it? vitational effect on moving things. By mapping the detailed transits in front of its star, as seen by growth and kinematics of galaxies out to high redshifts, we can us. First claims of direct imaging of planets observe dark-matter structures in the process of formation. have already been made using 8–10-m What is dark energy? Does it evolve? Direct mapping of space-time, using the most distant possible trac- telescopes (see Figure 2): it is only a mat- How many types are there? ers, is the key to defining the dominant form of energy in the Uni- ter of time until several reliable detections verse. This is arguably the biggest single question facing physical science. are available. Quantitative studies will Extending the age of discovery In the last decades astronomy has revolutionised our knowledge of become possible with advanced adaptive the Universe, of its contents, and the nature of existence. The next optics, using coronographic techniques to big step is likely to be remembered for discovering the unimagined suppress the glare from the planet’s new. parent star. Studies of Earth-like planets, especially via spectroscopy, will however remain impossible. Extremely Large Telescopes offer spec- tacular advances in studying planetary systems. In addition to the improved col- lecting area, needed for observing such Figure 2: Infrared image obtained with 2MASSWJ1207334-393254 faint objects as the smaller extra-solar the NACO adaptive optics facility on the VLT of the young (~ 10 Myr) brown planets, the improved resolution allows dwarf 2M1207 (centre) in the nearby cleaner separation of a planet from TW Hydrae association (Chauvin et al. the image of its star. As a result, one of 2004). The fainter object seen near it the most exciting new opportunities at an angular distance of 778 milliarc- sec has recently been confirmed to be for Extremely Large Telescopes is the abil- gravitationally associated with the ity directly to detect and to study large brown dwarf. Models suggest that it is samples of planets in other solar systems. a giant exoplanet with a mass about five times that of Jupiter. The source is very young, is still liberating consider- Planets of course come in a wide range able energy as it contracts and cools, of types, sizes and distances from their and probably formed in a way unlike parent stars. What sort of planets can be that of planets in our Solar System.