Academic Reading — Test 130

Reading passage

A radio telescope does not capture light in the way a familiar optical instrument does. Instead, it gathers the long, faint radio waves that pour out of stars, galaxies and clouds of cold gas spread across the universe. Because these signals are extraordinarily weak by the time they reach the Earth, the surface that collects them must be enormous. The Square Kilometre Array, usually shortened to the SKA, takes its name from an early design target: a collecting area approaching one square kilometre. No single dish of that size could ever be built, so the engineers chose a different route. Rather than constructing one colossal structure, they decided to link many smaller antennas together and combine their signals, a method that allows a network of modest instruments to behave, in effect, like one gigantic telescope. This approach is known as interferometry. When the output of separated antennas is combined with great precision, the resolution of the resulting image depends not on the size of any individual dish but on the distance between the most widely spaced antennas. For this reason the SKA spreads its receivers across vast distances, with some stations placed hundreds of kilometres apart. The further apart the antennas sit, the finer the detail the array can resolve. The trade-off is that the timing of every signal must be controlled to within a tiny fraction of a second, because the data streams have to be aligned as though they had all arrived at a single point. Achieving this demands atomic clocks and an unbroken web of optical fibre carrying information between the stations. The project is unusual in that it is divided between two widely separated countries. One portion is being built in the remote interior of Western Australia, where low-frequency signals are gathered by tens of thousands of simple, motionless aerials that resemble metal Christmas trees rather than conventional dishes. The other portion is situated in the arid Karoo region of South Africa, where hundreds of steerable dishes collect signals at higher frequencies. Both locations were chosen for the same overriding reason: they are among the quietest places on the planet in radio terms. Far from cities, mobile-phone masts and busy airports, these sites suffer very little of the human-generated interference that would otherwise drown out the delicate cosmic whispers the telescope is designed to hear. Protecting this silence is itself a continuous engineering challenge. Ordinary electronic equipment leaks radio noise, and even a laptop or a digital camera operating near the antennas can swamp a signal that has travelled for billions of years. To prevent this, much of the on-site computing is enclosed in shielded chambers, and strict limits are placed on the devices that staff may bring into the core of each array. Governments have also designated large surrounding zones in which new transmitters are tightly restricted, creating a buffer of quietness around the instrument. None of these measures eliminates interference entirely, but together they reduce it to a level the system can tolerate. Perhaps the most demanding part of the SKA is not the antennas themselves but the torrent of data they generate. When thousands of receivers observe the sky at once, they produce raw information far faster than any existing network could transmit it across the world. The answer is to process the data close to where it is collected. Powerful computers known as correlators combine the incoming streams on site, while supercomputers reduce the flood to a manageable volume before anything is sent to astronomers abroad. Even after this drastic reduction, the array is expected to archive enormous quantities of scientific data every year, posing storage problems that engineers are still working to solve. In this sense the SKA is as much a computing project as an astronomical one. The scientific rewards are intended to justify the difficulty. Researchers hope the array will trace how the first stars and galaxies formed after the early universe emerged from a long dark age, test theories of gravity using the precise ticking of distant pulsars, and search for the faint chemical signatures of life-supporting molecules in space. Because the instrument is so sensitive, it may also reveal phenomena that no one has yet predicted, which many astronomers regard as the most exciting prospect of all. Building it, however, will take decades and the cooperation of many nations, each contributing money, expertise and engineering talent. The SKA therefore stands not only as a scientific instrument but as a test of whether countries can sustain a shared technical endeavour over a span of time longer than most careers.