The largest single optical telescope in the Southern Hemisphere and one of the largest worldwide, SALT received the award in the category of International STI Partnership Achieving Excellence in Global Science. Known affectionately as Africa’s Giant Eye on the Sky, SALT is a powerful symbol of international scientific cooperation, with eight current shareholder partners including leading universities, science organisations, and funding agencies from Africa, India, Europe, and North America. It is based in Sutherland, Northern Cape, at the South African Astronomical Observatory (NRF-SAAO), a facility of the National Research Foundation. The NRF, funded and supported by the Department of Science, Technology and Innovation (DSTI), is the principal shareholder and is responsible for the maintenance and operations of SALT through NRF-SAAO. This multinational partnership continues to strengthen SALT’s scientific output through shared expertise, postgraduate training opportunities, student exchange programmes, and wider societal impact realised through its SALT Collateral Benefits Programme.

This latest accolade for SALT comes hot on the heels of the 20th anniversary celebrations of its astronomical excellence and breakthroughs on 10 November. For over two decades, SALT has delivered groundbreaking global research and accelerated South Africa’s contribution to modern astrophysics. The facility has produced more than 600 peer-reviewed scientific publications, including a milestone of over 80 publications in 2024 alone.

Among numerous science highlights, in August 2017, SALT produced one of the world’s first optical spectra associated with a gravitational wave event—marking the dawn of multi-messenger astronomy. This breakthrough continues to shape the South African National Multiwavelength Strategy and future scientific direction for the next decade and beyond.

“I would like to congratulate the SALT team for this well-deserved award. SALT’s success story is one of national pride and aspiration. Its iconic silver dome rising above the Karoo hills symbolises South Africa’s determination to look upward and forward. Through its education, outreach, and research programmes, SALT has inspired countless young people to pursue careers in science, technology, engineering, and mathematics (STEM). The telescope’s visibility in media, tourism, and education continues to capture the public imagination. It is a living example that science belongs to everyone and that major discoveries can emerge from African soil,” said Dr Mlungisi Cele, Director-General, DSTI.

Receiving the award, Prof Rosalind Skelton, SALT board member and Managing Director of NRF-SAAO, said, “SALT is a catalyst for SA’s leadership in astronomy, enabling world-class research and fostering meaningful partnerships across borders in pursuit of shared scientific discovery.”

SALT’s influence reaches well beyond its scientific achievements. It has helped cultivate a vibrant community of African astronomers, engineers, and data scientists, laying the groundwork for sustained excellence in the region. Its success was pivotal in securing South Africa’s role as host of the SKA-Mid telescope—a testament to the country’s growing stature in global big science and its commitment to collaborative innovation.

The SFSA Science Diplomacy Awards celebrate individuals, organisations and institutions demonstrating outstanding commitment to advancing science diplomacy—those whose work contributes meaningfully to the intersection of scientific research, international cooperation and partnerships, policy development, evidence-based decision-making, and diplomacy with a footprint in the regional and global science community.

NRF-SAAO MD Dr Rosalind Skelton receiving the award.

Artist’s impression of a supersoft X-ray source: the accretion disk around a white dwarf star is made mainly of helium. © schematics: F. Bodensteiner; background image: ESO

White dwarfs can only explode as supernovae when their mass exceeds a certain limit. One of the primary aims of this research was to understand the process by which the mass of a white dwarf can grow to this point, known as the Chandrasekhar limit. The team found that [HP99] 159, unlike other known Super Soft Sources (SSS), was overflowing and burning helium, not hydrogen, which had not been observed before in such detail.

Using SALT’s two spectrographs, the team was able to determine that the optical spectra of the system were entirely consistent with helium accretion. The measured luminosity suggests that the mass of the white dwarf is growing more slowly than previously thought possible, which could potentially help understand the number of supernovae caused by exploding white dwarfs.

“This demonstrated the uniqueness of this object, but also the capability of SALT’s two spectrographs allowing for the required detailed follow-up optical observations, confirming the nature of the source ”, said Dr Itumeleng Monageng.

Low-resolution optical spectrum of [HP99] 159, taken with the SALT/RSS spectrograph, with labels for the main emission lines, which are all due to helium. (The two ‘bkg’ labels are residuals of removing sky lines). The insets demonstrate that at two wavelengths, where He- and H-lines are close together, the signal results from He II and not hydrogen.
© MPE

The unique properties of [HP99] 159 suggest that it could end up in a subclass of SN Ia, known as SN Iax, which have weaker explosions and therefore less helium is blown away. The team hopes to find dozens of similar sources in the two Magellanic Clouds with the eROSITA telescope, which could help further constrain the conditions for SN Ia progenitors.

“This is another excellent example of the productive collaborations between our team and the German eROSITA team in discovering and studying new and interesting transient phenomena,” said Prof David Buckley at the South African Astronomical Observatory (SAAO), who leads the SALT transient programme for which the optical observations were obtained, and with, Dr Monageng, is one of the paper’s co-authors.

Original press release

https://www.mpe.mpg.de/7938487/news20230322

Reference

J. Greiner, C. Maitra, F. Haberl, R. Willer, J. M. Burgess, N. Langer, J. Bodensteiner, D. A. H. Buckley, I. M. Monageng, A. Udalski, H. Ritter, K. Werner, P. Maggi, R. Jayaraman & R. Vanderspek: A helium-burning white dwarf binary as a supersoft X-ray source. Nature 615, 605-609 (2023) (View)

Trajectories within the quadruple stellar system HD 74438: the two close pairs, having orbital periods of 21 and 4 days, orbit around each other in 6 years. At some point, the two pairs could merge into white dwarfs giving rise to a thermonuclear supernova, as illustrated in the bottom right. (Image Credit: Merle, A)

Stars like to be in company, and unlike our Sun, most of the stars in the Galaxy have one or more stellar companions. Binary stars are now recognized to play a major role in a large range of astrophysical events, such as the 2017 gravitational wave emission detection. In addition, binary stars allow us to derive fundamental stellar parameters like masses, radii and luminosities with better accuracy compared to single stars. They represent the gems on which various astrophysics studies rely.

While binaries have received much attention so far, higher-order stellar systems have remained aside until recently, despite the fact that they show a wide variety of interactions, especially in tight systems. Stellar quadruples only represent a marginal fraction (a few percent) of all multiple systems. The complex evolution of such high-order multiples involves mass transfer and collisions, leading to mergers that are also possible progenitors of thermonuclear supernovae. These supernovae represent standard candles for fixing the Universe distance scale, despite the fact that the evolutionary channel(s) leading to the progenitors of such supernova explosions are still highly debated.

A spectroscopic quadruple (HD 74438) was discovered in 2017 in the Gaia-ESO Survey. The Gaia-ESO Survey is a public spectroscopic survey providing a detailed overview of the stellar content of the Milky Way by characterizing more than 100 000 stars. Subsequent follow-up spectroscopic observations of HD 74438 were obtained with high-resolution spectrographs at the University of Canterbury Mount John Observatory in New Zealand and at the Southern African Large Telescope in South Africa. These observations allowed us to determine that this stellar quadruple is made of 4 gravitationally-bound stars: a short-period binary orbiting another short-period binary on a longer orbital period (2+2 configuration). Its membership in the open cluster IC 2391 makes it the youngest (43 million years) spectroscopic quadruple discovered so far and among the quadruple systems with the shortest outer orbital period (6 years).

Thanks to the spectroscopic analysis it was possible to show that this quadruple system is undergoing dynamic effects on long time scales compared to the orbital periods. Indeed, one of the inner binaries should have evolved into a circular orbit whereas it has an eccentric one. This is explained by the gravitational effect of the distant binary companion which can pump up the eccentricity. State-of-the-art simulations of this system’s future evolution show that such gravitational dynamics can lead to one or multiple collisions and merger events producing white dwarfs with masses just below the Chandrasekhar limit.

A star like our Sun will end its life as a white dwarf, and the mass of white dwarfs cannot go above the so-called Chandrasekhar limit. If it does, as a result of mass transfer or merger events, it does collapse and produces a thermonuclear supernova. Interestingly, 70 to 85% of all thermonuclear supernovae are now suspected to result from the explosion of white dwarfs with sub-Chandrasekhar masses. The evolution of stellar quadruples such as HD 74438 thus represents a new promising channel to form them.

Reference

1. Merle, A. S. Hamers, S. Van Eck, A. Jorissen, M. Van der Swaelmen, K. Pollard, R. Smiljanic, D. Pourbaix, Tomaž Zwitter, G. Traven, G. Gilmore, S. Randich, A. Gonneau, A. Hourihane , G. Sacco and C. C. Worley

A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae 

Nature Astronomy, Letters https://doi.org/10.1038/s41550-022-01664-5

Photograph of Nova V906 Carinae taken at the Onjala observatory in Namibia. The nova is the star to which the two faint lines are pointing. Credits: W. Paech & F. Hofmann, Chamaeleon and Onjala Observatory, Namibia).

An international team of researchers, led by Dr Elias Aydi, a former SAAO and University of Cape Town PhD Student, now at Michigan State University (MSU), have discovered a new cause for the incredible brightness observed when a star explodes. The discovery used high-resolution optical spectroscopy from different telescopes including SALT to better understand the stellar explosion or nova.

A nova is an explosion on the surface of a star that can produce enough energy to increase the star’s brightness by millions of times. Sometimes a nova, which occurs in stars called white dwarfs, is so bright it appears as a new star to the naked eye. A white dwarf star strips material from its companion star that piles up on the dwarf’s surface, eventually triggering a thermonuclear explosion.

While for many years astronomers have thought that nuclear burning of material on the surface of the white dwarf directly powered all the light from the explosion, more recently astronomers started debating that “shocks” from the explosion might power most of the brightness.

The research is detailed in a paper published in the journal Nature Astronomy titled “Direct evidence for shock-powered optical emission in a nova.”

“This is a new way of understanding the origin of the brightness of novae and other stellar explosions,” said Elias Aydi, a research associate in MSU’s Department of Physics and Astronomy, who led an international team of astronomers from 40 institutes, across 17 countries. “Our findings present the first direct observational evidence, from unprecedented space observations, that shocks play a major role in powering these events.”

The SALT observations were taken under the transient follow-up programme, with Dr David Buckley at SAAO being the Principal Investigator. Nova became an important class targeted by the programme since 2016, led by Dr Aydi, who was a graduate student at the time. It now involves a number of different co-investigators from 3 of the SALT partners (South Africa, USA and Poland) plus many other international collaborators.

More details can be found in the MSU press release, which this article has been adapted from.