The Square Kilometer Array: Astronomy for the Next Millennium

Progress in astronomy has always depended on cutting edge instruments with greater resolving power and sensitivity to reach farther into the universe, and to detect new kinds of objects with unexpected properties. The radio telescopes of the past decades have explored the electromagnetic spectrum far from the traditional optical wavelengths, and have achieved a striking series of discoveries such as pulsars, quasars, gravitational lenses, radio galaxies, and the cosmic microwave background. These have, in turn, proven to be fruitful sources of knowledge about gravitation, nuclear matter, the interstellar medium, and high energy phenomena, and have contributed significantly to cosmology. These new discoveries lead to the conclusion that major advances in knowledge can be expected from a new radio telescope, two orders of magnitude more sensitive than any existing instrument, with a collecting area of one square kilometer.

International studies, including groups in Australia, Canada, China, India, the Netherlands, and the US are examining concepts of such an instrument, generally referred to as the SKA. The scientific advances that can be expected include many urgent topics at the forefront of astronomy. These include cosmology, cosmogony, high-energy astrophysics, fundamental physics, and a wide range of specific topics, including pulsars, X-ray binaries, and exo-planetary systems. A few brief examples can be cited to indicate the fundamental quality of the research that would be done with the SKA. At the lower frequency range the dawning of the universe can be explored, beyond the epoch of galaxy formation at redshift 5-10, and the dynamics of the earliest galaxies can be both determined and tracked through time to the present epoch. At the high-frequency range of the SKA, molecular lines in the interstellar medium of primitive galaxies can be measured, and the origin of the heavy elements can be studied during the earliest epoch of galaxy formation between redshift 4 and 5. The existence of black holes in the nuclei of galaxies can be explored by observing megamasers, which have proven to be the most powerful tool so far in pinning down the masses of black holes. A more complete list is appended.

The scientific specifications, taking technical feasibility into account, indicate that the operating range should be approximately between wavelengths of 2 meters and 1.5 centimeters (150 MHz to 20 GHz) The array would draw upon advances in solid-state technology, communication capability, and computer power. All of these fields have engineering interest for academic scientists and engineers. The array would be interferometric, not monolithic, and its nominal maximum dimension at present is in the range 300 to 1000 kilometers. Radio interferometry is a field in which US radio astronomers have played a leading role, and the SKA builds logically on that tradition. The project will almost certainly be international. Present estimates of the overall cost are in the range of $1 billion, with the US share likely to be about one-third of the total.