Research Themes

Time Domain, Transient Science and Stellar Astrophysics

Time-domain astronomy, of which transient science is a sub-field, has a long history in SA. SAAO astronomers study binary stars, pivotal to the development of accretion theory, using many different Sutherland telescopes and instruments. Many SAAO and SALT instruments boast high-time-resolution capabilities in photometry, polarimetry and spectroscopy, making this a unique strength of SAAO astronomy.

The evolution of binary systems leads to exotic inhabitants of our Galaxy, such as black-hole binaries, cataclysmic variables, novae, symbiotic stars, binary central stars of planetary nebulae, supernovae, luminous blue variables, and even the further distant gamma-ray bursts. Many of these phenomena are targets of active current SAAO research, using both observations and theoretical work with super-computers. Extremely energetic events test the laws of physics under conditions unavailable in laboratories or particle accelerators and offer a rich source of truly new discoveries. Some of the classes of transients, such as tidal disruption events or stellar and compact object mergers, are rare and still quite mysterious, needing large surveys to establish defined samples.

SAAO transient research draws on survey data from many ground-based and space projects, including MASTER-Net, ASAS-SN, PanSTARRS, Skymapper, Gaia, Swift, Fermi, MAXI, and from many wavelengths (radio, infrared, optical, X-ray, gamma-ray). In the near future, MeerKAT and MeerLICHT will be the most important sources of transient detections, followed in a few years’ time by the LSST and SKA. The transient astronomy group at SAAO works together to act on alerts for follow-up observations, and it also coordinates the only Large (and multi-partner) Science Project on SALT thus far.

Because of the MeerLICHT/MeerKAT connection, and especially the future LSST and SKA promise, transient science is bound to be a key field of future astronomy. Moreover, in an exciting new area of multi-messenger astronomy, rare gravitational wave events are detected by LIGO/Virgo, or neutrinos from large international detectors such as ICECUBE. Both are right at the cutting edge of physical science. For these reasons, the SA community placed their highest priority request for a new extremely high-efficiency spectrograph on SALT as its fast-tracked “1.5 generation” instrument.

For SAAO to not only remain a player in the field but to offer something unique in the world, we have started The Intelligent Observatory Project, envisioning a future where the whole Sutherland observation station is transformed into a giant networked transient machine. This will require major investment in software development due to the deluge of candidates expected in the LSST era, the need for automated data reduction and classifications of spectra, and automated and intelligent triggers for the next layer(s) of telescopes and instrument modes available to further characterise the most interesting targets. First steps into this project have already started with the successful modernisation of some of our older telescopes to be remotely controlled from Cape Town. More observations will happen remotely in the future, and fully autonomously as well in further steps of the project, responding to the needs of big data and extremely rapid time scale of events.

Galaxy Evolution and the Baryon Cycle

Galaxies grow through a combination of accretion of dark matter and its associated gas, and through mergers. Major mergers that involve galaxies of similar size are the most spectacular examples of such a process, but interactions with the much more numerous dwarf galaxies are more common. All these interactions allow SAAO researchers to test models of galaxy formation.

Over time galaxies accrete, eject and reaccumulate gas through what is known as the baryon cycle. The origins and properties of this cycle are complex and not well studied, but understanding the baryon cycle is crucial to understanding the birth, growth, and evolution of galaxies, and the triggering, feedback and fuelling of star formation within them.

SAAO astronomers are involved in numerous studies in galaxy evolution. SAAO instruments like SALT, IRSF and KMTNet are used to study nearby galaxies and their environments in detail to discover highly-evolved stars, determine chemical evolution and star formation histories of dwarf galaxies, and studying low-surface-brightness galaxies and intergalactic light. Other studies of slightly more distant galaxies target the dynamics of spirals using Fabry-Perot observations and study lenticular galaxies, disk galaxies, and galaxies in voids to decipher their histories and/or their dark matter content. SALT and other large telescopes world-wide, including space observatories and radio telescopes, are used to characterise the baryon cycle, gas outflows and accretion, central supermassive black hole growth, and violent star-formation in interacting galaxies.

SAAO astronomers use SALT to study merger rates of higher redshift galaxies, and to study the variability and characteristics of the active galactic nucleus (AGN). SAAO researchers are part of large international efforts to study the cosmic star-formation rate and impact of the environment in systems over half the age of the universe. Looking into the future, MeerKAT/SKA will study the widely-distributed reservoirs of neutral gas outside of galaxy disks, and together with optical measurements of ionised gas, SAAO astronomers will constrain models of accretion and outflow of gas, strengthening both science results and optical/radio collaboration in the country.

Several SAAO researchers are also involved with cosmological studies, especially those with joint positions with, or those collaborating with, African Institute for Mathematics and Science (AIMS), University of the Western Cape (UWC), or University of Cape Town (UCT). Cosmological observations at the SAAO exploit type Ia supernovae discovered as part of international collaborations for the Dark Energy Survey. In addition, the cosmology group is involved in both the LADUMA and MIGHTEE large-scale surveys on MeerKAT, and in various theoretical and software algorithm development initiatives.

Exoplanets and Planetary Sciences

Characterising the population of planets outside of the Solar System, and, ultimately, the search for habitable worlds, is the third focus area for SAAO science. SAAO researchers are involved with the PLANET microlensing survey, in an on-going exoplanets search with the Sutherland-based KELT project, and in planetary science more generally.

SAAO research will focus more strongly on exoplanet science in the future, for several reasons. First, the high-resolution spectrograph (HRS) on SALT is in principle suited for measuring radial velocities of exoplanets down to a few m/s accuracy. There are new space missions which require this type of follow-up observation (most notably the NASA/TESS mission), with only a handful of instruments globally that can do this currently (none of which are part of a 10m telescope). Second, over the next decades, there will be a shift from highest-profile astronomy missions concentrating on the deepest universe “origins” research, to finding life in the universe.

SAAO hopes to develop this research theme over the next few years, starting with exoplanet hunting and confirmation through HRS radial velocities; investigating possibilities to study the most nearby and/or brightest exoplanet candidate atmospheres with HRS; and also developing more collaboration with the exoplanet experiments already hosted at our site in Sutherland.

There is a small planetary astronomy research group  at SAAO. Recent research has concentrated on observing stellar occultations by Pluto, centaurs, and other large trans-Neptunian objects in order to measure sizes and study atmospheres and rings; as well as studies of asteroids, including near-Earth objects. Sutherland’s geographic location is important for this research, as is the high-speed instrumentation available on various SAAO/SALT facilities. The southern counterpart of the ATLAS observatory has recently been installed in Sutherland. This is a robotic telescope  developed by NASA to search for near-Earth objects.