The South African Radio Astronomy Observatory (Sarao), which is one of the National Research Foundation’s facilities, has announced that the country’s MeerKAT radio telescope array has made a major scientific discovery, solving a decades-old astronomical riddle. The discovery, recently published as a paper in the Astronomy and Astrophysics journal, was made by an international consortium of scientists, including South Africans, which was partly funded by the European Research Council.
The riddle concerned a galaxy designated NGC 1316 (NGC standing for New General Catalogue [of Nebulae and Clusters of Stars]), also known as radio galaxy Fornax A. It lies 60-million light years from earth and is both the brightest visible light and the most powerful radio-wave-emission galaxy in a cluster of galaxies in the constellation of Fornax. In fact, it is the fourth-brightest radio wavelength source in the whole sky.
NGC 1316/Fornax A was created a few billion years ago when two major galaxies (the smaller of which would have been about the size of our own galaxy, the Milky Way) collided, and then absorbed smaller satellite galaxies. But observation showed that the galaxy contained far less hydrogen gas than it should (hydrogen being the raw material for the creation and fuelling of stars).
“NGC 1316 contains a very large amount of dust in its interstellar medium,” pointed out Italian National Institute for Astrophysics Cagliari Observatory researcher and project lead author Paolo Serra. “It should also have contained an even greater amount of hydrogen. But, hitherto, no one had been able to detect anywhere near that amount of the gas.
“In this article, we show new radio images obtained with MeerKAT, which reveal where all the hydrogen was hiding – it’s distributed in two long, faint, gaseous tails, stretching to a large distance from the galaxy,” he explained. “[T]he tails were generated by tidal forces in action during the merger. “The amount of gas found is consistent with that expected, based on merger theory and on the fact that the smallest progenitor galaxy was like the Milky Way. Thus, thanks to these observations, all pieces of the puzzle are now in place, and we finally have a more precise and coherent understanding of the formation of this famous galaxy.” These hydrogen tails occupy the same locations as tails made up of stars.
“With this beautiful piece of work, Paolo and his colleagues, among whom are several young South Africans, have significantly advanced our knowledge of the formation and evolution of galaxies,” highlighted Sarao chief scientist Dr Fernando Camilo. “This provides a wonderful taste of what MeerKAT will do in years to come.”
Remarkably, the observations of NGC 1316 were carried out last year, while MeerKAT was still in its commissioning phase. (MeerKAT was formally inaugurated in July last year.) This resulted in only 40 of the array’s 64 dishes being available for the project. “Results like these show that MeerKAT has begun addressing some of the key open questions in modern astrophysics, and we look forward to researchers in South Africa and from around the world joining us on a journey of scientific discovery,” he affirmed.
MeerKAT’s dishes are spread over an 8 km diameter in the Karoo region of the Northern Cape province. However, 75% of the 64 dishes are concentrated within a diameter of just 1 km, forming a core for the instrument, while the remaining 25% are scattered more widely. “This was done on purpose to provide extra sensitivity for detecting the very faint radio signals that hydrogen atoms emit from across the universe, at a frequency of 1 420 megaHertz,” noted Camilo.