Credit: OLAF WUCKNITZ

To improve resolution, individual telescopes can be arranged into an array of telescopes. By means of interferometry the telescopes are then able to reach resolutions equivalent to that of a single enormous dish. At present, the largest such array is the Low Frequency Array (LOFAR). It is under construction across Europe and instead of individual telescopes — which would have to be very large to be sensitive to the long wavelengths measured — it employs array stations consisting of many low-cost antennas.

The figures illustrate the effect of long-baseline interferometry. With five stations spread across the Netherlands, the quasar 3C 196 looks like a featureless blob in the 4–10-m-wavelength range (left). Now add three stations in Germany, the farthest being near Munich: suddenly the resolution improves tenfold and details emerge (right); in fact, the image on the right zooms into the central region of the quasar, so the actual difference between the two images is a factor of 40. The quasar is a strong radio emitter, but even so, it is 7 billion light-years away.

LOFAR will soon include other stations, not to mention shorter-wavelength data, to further improve the resolution. In addition to probing mysteries of the early Universe, it will also have geophysical and agricultural applications.