The Southern African Large Telescope (SALT), based at Sutherland, in the Karoo region, in the Northern Cape province, is promising to become an important instrument for research into dark matter. "SALT is shaping up to be very important for answering questions about dark matter in the cores of galactic clusters," affirmed Michigan State University astronomer Professor Megan Donahue to Engineering News Online on Tuesday. "SALT has given us information we haven't be able to get any other way."

Donahue is a member of a major astronomical research programme, designated Cluster Lensing and Supernova survey with Hubble (CLASH).

Observations from SALT have contributed to this programme, although the main sources of data have been space telescopes.

CLASH has been made possible by the complementarity of the different types of space telescope now in operation. In addition to the Hubble Space Telescope, operating in the visual wavelengths, observations have also been taken from the Chandra X-ray Observatory, the XMM-Newton space telescope (also in the X-ray wavelengths) and the Spitzer space telescope (in the infrared wavelengths). Other ground-based telescopes have also assisted.

Among many other important discoveries, CLASH has confirmed important concepts regarding dark matter. This substance, about which almost nothing is known, makes up about 27% of our universe (the even more mysterious dark energy comprises some 68% of the universe) while conventional matter is responsible for less than 5%.

"CLASH is giving us the best maps of dark matter ever," she reported. "There was some worry that maybe we were missing something regarding dark matter in our earlier studies. There were some tensions between models and observations. What we wanted to test was if observations of a properly selected sample of galactic clusters would resolve these tensions. With a well-chosen random sample we are getting results closer to what we expected. So the theory has survived the experimental test!"

Currently, dark matter -- so called because it neither reflects nor absorbs light, and so is invisible -- is conceived as being composed of slow-moving, therefore "cold", particles and so is referred as CDM (cold dark matter) for short. When dark matter was first conceived, there was no indication what it would be like: it could, for example, have been "hot" (fast-moving).

"The concept of CDM has survived all the experiments and observations. The alternative concepts of dark matter -- for example, hot dark matter -- have not," explained Donahue. "CLASH results are essentially confirming that dark matter is made of cold particles. We've never found one in a laboratory -- yet."

Donahue presented a plenary session paper at the 2014 South African Institute of Physics conference at the University of Johannesburg on Tuesday.