South Africa’s giant eye on the sky - the Southern African Large Telescope (SALT) near Sutherland, Northern Cape.
Image: https://www.salt.ac.za/
By Vanessa McBride
THE SOUTHERN African Large Telescope (SALT) this week celebrates 20 years of observing the sky. SALT is the largest optical telescope in the southern hemisphere, built on a plateau near the town of Sutherland in the Northern Cape. It’s been steadily revealing new scientific knowledge, ranging from the discovery of planets outside our solar system to understanding the unusual physics around black holes. It’s also 20 years of doing science for society.
SALT is where I conducted much of my PhD research. I’d grown up in rural Eastern Cape, marvelling at the diamond night skies. My first fascination for astronomy was sparked when learning about the concept of SALT at a science fest in high school. Years later, I received the first SALT Stobie scholarship for PhD study. It was a dream opportunity to start a multi-year observing campaign.
My research sought to understand how mass moves from one star to another in a gravitationally bound pair. This contributed to the scientific understanding of how these stars evolve in different environments. So it’s with a sense of personal, professional and national pride that I look back on the last two decades of SALT’s achievements.
One of SALT’s most significant scientific achievements was based on its ability to respond rapidly to time-critical astronomical events. This allowed SALT to observe the immediate optical glow from a gravitational wave event in 2017, providing a crucial piece of evidence for the type of nuclear processes taking place in the gravitational wave event.
Gravitational waves are ripples in spacetime caused by moving masses, and have only been observable with special detectors since 2015. The plateau on which SALT is built is one of the darkest observing sites in the world. This makes it an excellent site from which to observe very low-brightness objects in the night sky.
In 2022, SALT observed a nearby but faint galaxy, which showed unusually low levels of elements heavier than hydrogen. This unexpected result challenged our understanding of how and when stars begin to form within galaxies. With a repertoire of over 600 scientific publications based on observations from the telescope, SALT has certainly made an impact on our knowledge of the cosmos.
Funded by a consortium of international partners, which was led by South Africa’s National Research Foundation, SALT represented an increase of 30x in light-gathering capacity compared to the Radcliffe telescope – the previous biggest in South Africa. At the concept phase, even astronomers had to be encouraged to think big. The original plans were for a 4 metre class telescope, but it was not audacious enough for a government that wanted to showcase South Africa’s prowess and potential in science.
Engineers and scientists worked with the Hobby-Eberly Telescope in the US to replicate a unique and cost-effective design. Smaller mirror segments were easier and cheaper to manufacture to the required smoothness specifications, and these smaller hexagonal segments could fit together like a honeycomb to create a mirror of 11 metres in diameter. The telescope was designed to point at a fixed angle above the horizon. This meant less warping of the mirror, but a more complicated observing strategy, as astronomers would have to wait for sky to pass over SALT’s pointing direction.
SALT was conceived just as South Africa was coming out of the shadow of apartheid. In 1996 the new government had written an ambitious white paper setting out a vision for science in a country reborn, where it felt like anything and everything was possible:
Scientific endeavour is not purely utilitarian in its objectives and has important associated cultural and social values. It is also important to maintain a basic competence in ‘flagship’ sciences such as physics and astronomy for cultural reasons. Not to offer them would be to take a negative view of our future - the view that we are a second-class nation, chained forever to the treadmill of feeding and clothing ourselves.
SALT has always been more than just a science infrastructure project. It has heart too. Unemployment is a major issue in Sutherland. Foetal alcohol syndrome is also a challenge people battle with in the region, and, through the years of its construction, South Africa was deep into the HIV/Aids epidemic.
Alongside the investment in engineering and science, was a plan to ensure benefit to previously disadvantaged South Africans, especially the rural community in the Northern Cape. Even today, 20 years after SALT was inaugurated, a fraction of the operation costs that are contributed by all SALT partners, local and international, go into this collateral benefits programme.
The results are a library, skills training centre and a high school mathematics and science teacher in Sutherland. Most recently, the SALT partners and South Africa’s Department of Science, Technology and Innovation have contributed to a renovated trauma room for victims of gender-based violence in the Sutherland police station. In its early years, this programme also trained astronomers through the funding of graduate programmes.
Now, this new generation of South African scientists and engineers is at the helm. For the first time in the 200-year history of the South African Astronomical Observatory, the director is South African. Almost 80% of the staff employed in all roles across SALT, from science and operations to software and mechanical, is South African. These individuals are deeply embedded in, and leading, international science partnerships and research infrastructure projects, and the connection between science and societal development is ingrained in the DNA of these projects and partnerships.
We are often focused on the differences between “us” and “them”; it’s worth remembering the power of science, both as a mechanism for development and as a partnership to unite. This World Science Day for Peace and Development, SALT shows the capabilities science has for both peace, and development.
* Vanessa McBride, Science Director at the International Science Council and Adjunct Associate Professor at the University of Cape Town.