New Eyes, New Skies

The next 40 years will see telescopes that far outstrip any ever seen before. Jeff Kanipe profiles two of them.

(from Nature Vol 457 Jan 5th 2009)

The armillary and astrolabe are now seldom seen outside museums and antique shops; but the telescope, which joined them in the observatories of early modern Europe 400 years ago, is still at the centre of the astronomical world. In optical precision, in the wavelengths that are used and in their sheer size, they have changed almost beyond recognition.

After two centuries in which they left no records other than the users’ sketches, and a century in which their visions were recordedon photographic plates, they have in the past decades become entirely electronic. And they are now stationed everywhere — oceans, deserts, mountain tops and all kinds of orbit. But the job is still the same: collecting and focusing whatever information the Universe sends our way. Yet for all its glorious 400-year history, the astronomical telescope’s best days may still be to come.

Telescopes currently in development show an unprecedented degree of technical ambition as they seek to provide near-definitive answers to questions that, a generation or two ago, it was hard to even imagine investigating. To answer these questions, the telescopes profiled here will often work in complementary ways.

The infrared capabilities of the James Webb Space Telescope and the radio acuity of the Square Kilometre Array will both be used to probe the Universe at the time of its own ‘first light’ — the birth of the first stars and galaxies. The radio array will map the large-scale structure of the Universe, elucidating the role in that structure of ‘dark matter’ and ‘dark energy’, as will studies of the faintest galaxies by the Large Synoptic Survey Telescope and European Extremely Large Telescope.

That behemoth and the orbiting Webb will, in turn, complement each other in their attempts to characterize planets around other stars with unprecedented detail. This quartet, for all its ambition and expense, does not exhaust the possibilities being explored and wished for. The Atacama Large Millimeter/Submillimeter Array will soon revolutionize astronomy at its chosen wavelengths.

Other projects are planned throughout the electromagnetic spectrum and beyond into the new realms of gravitational waves and neutrinos. These instruments are all being designed with specific scientific challenges in mind. But at the same time, all concerned hope devoutly to discover something as strange and unlooked for as Galileo’s mountains on the Moon — or spots on the face of the Sun.

The James Webb Space Telescope

Like the Hubble Space Telescope, to which it is in some ways the successor, the James Webb Space Telescope (JWST) will be the orbital flagship of its generation. But whereas the Hubble sees mainly in the visible and ultraviolet, JWST is optimized for the infrared. That means it can see things hidden from the Hubble and ts like by dust, and peer into the high-redshift epoch just after the Big Bang at objects indiscernible at visible wavelengths — such as the first stars.

Astronomers at the Space Telescope Science Institute in Baltimore, Maryland, started their first plans for a follow-on instrument in 1989 — a year before the Hubble itself was launched. It should finally make it to the launch pad 24 years later. Although its design and cost have changed a few times over the past two decades (see Nature 440, 140–143; 2006), its main mission remains simple and visionary — to study unseen aspects of every phase of the history of the Universe. To do so, the telescope will make use of several innovative technologies, such as ultra-lightweight optical systems made from beryllium, extremely sensitive infrared detectors and a cryocooler that can maintain the mid-infrared detectors at a frosty 7 kelvin indefinitely.

The most striking of the new technologies, though, affects the very heart of the telescope.
JWST’s designers wanted a mirror that would have been too large to fit into the payload fairing of any rocket available. So they designed one in segments, a mirror that could be launched folded up and then deployed to its full 6.5-metre diameter once the telescope settles
into its final orbit, 1.5 million kilometres from Earth. That distance gives the telescope
much more sky to look at than the Hubble gets, and keeps it cooler, too. But it has its
downside: as yet there is no way to get there to ix any problems so, unlike, the Hubble, JWST has to work perfectly from the start.

At the moment, says John Mather, Nobel laureate and senior project scientist for JWST, the telescope is designed to last for at least five years, but longer may be possible. It will carry ten years’ worth of fuel, and the presence of the cryocooler means that, unlike earlier infrared missions, its lifetime is not limited by a fixed supply of coolant. “If we are lucky and clever we hope to conserve fuel and perhaps run much longer,” says Mather. “But we can’t promise that.” What Mather thinks he can promise is discovery. “We do not know which came first, black holes or galaxies, and we do not know how it happens that there is a massive black hole at the centre of almost every massive galaxy. If there are any surprises about the early Universe, I am guessing that they will be in these areas.”

JWST is not just about deep space and distant epochs, though; it will also scrutinize the shrouded origins of objects closer to home — such as nascent solar systems, coalescing stars and star clusters amassing within dusty nebulae, says Matt Mountain, director of the Space Telescope Science Institute. But where the telescope will really stand out will be its ability to probe the very early Universe. “JWST is so sensitive,” says Mountain, “that we can take

actual spectra of the very earliest objects you can just barely detect with Hubble.”

The Large Synoptic Survey Telescope

Sometimes telescopes see double not because of aberration, but because that is the way the Universe works. The bending of light by intervening masses — called gravitational lensing — means that some galaxies are seen by Earthly observers in more than one place. By adding together survey image after survey image, and so measuring things that no individual image would show, the designers of the Large Synoptic Survey Telescope (LSST) hope to find a significant fraction of the 10,000 or so such images in every square degree of sky. They also hope to open up a neglected dimension in astronomy: time. As well as adding together images of the same part of space taken again and again to reveal new depth, they will compare those images to spot any differences, turning up a wealth of supernovae, asteroids and Kuiper belt objects on the fringe of the Solar System that would otherwise be missed. The telescope’s proponents call it celestial cinematography.

The telescope will suck in celestial data by the terabyte every night, surveying almost
all of the sky visible from Cerro Pachón, Chile, every week. Such coverage is made possible by an 8.4-metre primary mirror, which will be ground so as to provide a field of view of 10 square degrees. That’s 49 times the size of the full Moon, and more than 300 times the field of view of the Gemini telescopes, which have mirrors of similar size optimized for staring in a single spot.

Over ten years, says Željko Ivezič, of the University of Washington in Seattle, the LSST system will look at everything in its field of view about 1,000 times. A massive amount of computing power will be used to correlate, compare and catalogue the torrent of data — and to make them all available on the Internet. Anyone with a computer — students, and amateur and professional astronomers — will be able to participate in the process of scientific discovery. Studies of objects that have been gravitationally lensed should reveal huge amounts about the structure of the Universe in general, and the distribution of dark matter and the effects of dark energy in particular. At the same time, though, LSST will mount a virtual space patrol, looking for potentially hazardous near-Earth asteroids. Astronomers already know where most of the big, killing-off-species-wholesale asteroids are.

LSST will be one of the tools that catalogues the vast majority of lesser asteroids still capable of smashing a city. But with a sensitivity to faint, transient events 1,000 times greater than ever previously achieved, the telescope will not restrict itself to the ‘vermin of the skies’ in Earth’s backyard. It will observe vast distant cataclysms, such as collisions between neutron stars, and is all but sure of discovering whole new categories of transient events.

The project is overseen by the LSST Corporation, comprising more than 100 scientists and two dozen laboratories, universities and institutes based mainly in the United States. Although the project’s design is still being worked out, the main mirror has already been cast. Astronomers with the corporation are hopeful that construction will begin as planned in 2011 and that first light will occur in 2015. In the subsequent ten-year survey, LSST will take stock of every object in the Universe, known, unknown and newly discovered. “For the first time in history,” says Ivezič, “we will catalogue and study more celestial objects than there are people on Earth.