South Africa’s ‘Giant Eye on the Sky’ celebrates its 20th anniversary

SUTHERLAND – The Southern African Large Telescope (SALT), nicknamed Africa’s Giant Eye on the Sky, is celebrating the 20th anniversary of its inauguration. SALT is the largest single optical telescope in the Southern Hemisphere and amongst the largest in the world.

SALT’s 11 metre telescope can detect the light from distant objects in the universe, a billion times too faint to be seen with the unaided eye.

A celebration event will take place on 10 November at the South African Astronomical Observatory (SAAO) site in Sutherland in the Northern Cape, where SALT is located and operated. This was announced by the National Research Foundation (NRF).

In the late 1990s, South Africa’s scientific leaders presented an ambitious vision: to construct a 10-metre-class optical telescope in the Southern Hemisphere as a flagship for the new South Africa. In June 1998, the South African government committed US$10 million toward this dream.

Construction was completed in 2005, followed by a commissioning and performance verification phase from 2006 to 2009. Since September 2011, full scientific operations have been underway, with the telescope now fully realising its vast potential as Africa’s Giant Eye on the Universe.

The NRF-SAAO stated in its motivation that SALT “…would enable South Africa to remain internationally competitive in astronomy well into the 21st century and furthermore provide a focus for the development of basic space science on the African continent”.

Astronomical milestones

SALT announced several astronomical milestones over the years, including:

• Kilonova of GW170817 (2017): SALT took part in the first multi-messenger event. It was among the first telescopes to observe the optical afterglow of the first detected neutron star merger, obtaining a crucial, early spectrum of the kilonova associated with the gravitational wave event GW170817. These data helped confirm heavy element synthesis models in the merger ejecta – a landmark in multi-messenger astronomy.
• Exoplanet microlensing (2019): SALT played a crucial role in a campaign that used gravitational microlensing to discover new exoplanets. For instance, SALT spectroscopy supported the characterisation of a short-period exoplanet detected by the Korean Microlensing Telescope Network (KMTNet), demonstrating SALT’s strength in rapid follow-up of transient planet signals.
• Eight super-hot stars unveiled (2020): Using SALT, astronomers identified eight new extremely hot subdwarf stars – rare helium-burning stars with surface temperatures over 100 000° on the Kelvin scale. These discoveries provided insight into late stages of stellar evolution, with SALT’s UV-sensitive spectroscopy proving crucial in the analysis of their atmospheres.
• “Peekaboo” galaxy discovery (2022): SALT helped characterise a tiny nearby galaxy nicknamed the “Peekaboo Galaxy”, which had only recently emerged from behind a fast-moving star. SALT spectra showed the galaxy has extremely low metallicity, akin to galaxies in the early universe. This finding, combining SALT and Hubble Space Telescope data, offers a unique local window into primordial galaxy conditions.
• Four-star multi-stellar system (2023): SALT, in partnership with the University of Canterbury’s observatory, discovered an unusual quadruple star system with two pairs of closely orbiting stars. SALT’s spectra confirmed the gravitational binding of the four stars, providing a testbed for theories of multi-star formation.

The 20th anniversary event will feature keynote addresses by NRF board chair, Professor Mosa Moshabela, and the deputy minister of Science, Technology and Innovation, Nomalungelo Gina, alongside prominent astronomers and international partners. The programme will showcase SALT’s scientific achievements, global partnerships, and contributions to the advancement of astronomy on the African continent.

National, international shareholders

SALT is owned by the SALT Foundation, a private company registered in South Africa. The shareholders of this company include universities, institutions and science funding agencies from Africa, India, Europe and North America.

The South African NRF is the major shareholder, owning approximately one-third of the shares. Just over half of the operating costs are currently covered by the NRF, ensuring that significant observing time is available to the South African community.

Other large shareholders are Rutgers University, the Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences, Dartmouth College, the University of Wisconsin–Madison, and the Inter–University Centre for Astronomy and Astrophysics in India. Smaller shareholders include the American Museum of Natural History and the UK SALT Consortium, with the latter currently representing Armagh Observatory.

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