At twin ground-breaking ceremonies today in South Africa and Australia, project leaders formally marked the start of construction on what will be the largest radio telescope ever built. Dubbed the Square Kilometer Array Observatory (SKAO) – referring to the total area the antennas and dishes will cover when complete – the telescope is not a single detector but rather a collection of them, connected across two continents using a technique known as interferometry (the same technique used by the Event Horizon Telescope, which took the first ever photograph of a black hole in 2019).
The Australian portion of the array, called SKA-Low, is designed to detect low frequencies from 50 to 350 megahertz, while the South African array, SKA-Mid, will manage frequencies from 350 megahertz to 15.4 gigahertz. SKA-Low will eventually consist of 131,000 antennas, each two meters in height and shaped like Christmas trees, while SKA-Mid will take the form of 197 large dishes.
One of the world’s most powerful existing radio telescopes, MeerKAT, will be incorporated into SKA-Mid towards the end of development. MeerKAT’s 64 dishes are already built on the South African site.
Six other countries have signed on to SKAO as partners: China, Italy, the Netherlands, Portugal, Switzerland, and the United Kingdom, with several other nations considering membership in the coming years.
First envisioned in the early 1990s, SKAO as a concept has been in development for decades, so today’s ceremony was a long time coming for many of the researchers involved.
SKAO Council Chair Dr. Catherine Cesarsky marked the beginning of construction in South Africa, saying “The SKA project has been many years in the making. Today, we gather here to mark another important chapter in this 30-year journey that we’ve been on together. A journey to deliver the world’s largest scientific instrument.”
But there’s still a long way to go before first light.
Construction is expected to last another decade, with the first ‘proof of concept’ coming in 2024, when six Australian stations and four South African dishes will be brought online for testing. By 2028, the collecting area will reach nearly 500,000 square meters, halfway to the square kilometer size eventually intended for the project. When finally finished, it will be the world’s most powerful radio telescope.
The science goals for SKAO are as ambitious as the construction project itself. While astronomers from any country will be able to apply for observing time, much of the telescope’s initial observation period will be dedicated to a set of pre-determined high priority science objectives. The SKAO board has identified 44 key objectives in eight categories. These categories are:
Cosmic Dawn and the Epoch of Reionization
Scientific priorities in this category will involve studying the Epoch of Reionization, a phase of the early Universe about 400 million years after the Big Bang when the hot, dense plasma had faded and the first bright objects appeared, ionizing the primordial gases. The Square Kilometer Array will be the first telescope powerful enough to see this early era of illumination clearly.
SKAO will carry out a detailed survey of pulsars in the night sky, giving astronomers a much larger sample size to work with than is currently available. Pulsars (rotating neutron stars) are incredibly useful for testing gravity in extreme situations. Particularly exciting would be finding a pulsar orbiting a black hole, enabling tests of fundamental principles in the theory of gravity.
HI refers to normal hydrogen gas, the most abundant element in the Universe. It makes up much of the interstellar medium, and observations of the hydrogen line can tell us about the formation of galaxies beyond our own, star formation closer to home, and the large-scale structure of the Universe (the cosmic web).
This refers to the study of short-lived astronomical events, usually high-energy bursts and that last from less than a second to perhaps weeks or months before fading. Goals in this category include observing black hole mergers in the electromagnetic spectrum at the same time as gravitational wave detectors, observing gamma ray bursts, and solving the missing baryon problem (in which there appears to be less normal matter – the stuff you and I are made of – than expected in the Universe).
Cradle of Life
This category refers to the study of exoplanets that might contain life, including the search for extraterrestrial intelligence via technosignatures, and measuring the abundance of pre-biotic molecules elsewhere in the Universe.
SKAO’s magnetism studies are interested in magnetic fields on the grandest scales. Researchers hope to understand how magnetic fields shape the cosmic web and the structure of matter and energy in the Universe writ large.
The cosmology goals focus on big questions about the Universe and its formation, including mapping dark matter/dark energy in radio frequencies, testing general relativity with high-precision measurements, and mapping the initial conditions of matter in the Universe.
Continuum refers to the spectrum of an object across a range of wavelengths. In this context, SKAO will examine star formation, as well as the role of black holes in galaxy formation. They will also look for gravitational lensing effects to probe dark matter and the high-redshift (ie. very old) parts of the Universe.
Also included in the final category is a recognition of the possibility of rare or serendipitous astronomical events. As an instrument that surveys the night sky broadly, rather than targeting particular objects, SKAO has a high chance of catching unexpected events and unique objects by accident. One of the technical challenges in making SKAO a reality is developing the processing power to dig through the masses of data it collects, and to pick out objects of potential interest.
All told, SKAO promises to usher in an exciting new era in radio astronomy. It’s still early days, and ‘first light’ is years away, but the sheer wealth of information SKAO will be able to collect when completed is enough to make any astronomy fan giddy.
SKAO report on science priority outcomes (see Appendix A for detailed breakdowns of each priority).