The Karoo-based MeerKAT radio telescope, located about 90 km from Carnarvon, in the Northern Cape, was inaugurated on July 13, giving the public a glimpse into what was unveiled as the best of its kind and a true benchmark in terms of pioneering scientific cosmic discovery, says South African Radio Astronomy Observatory (Sarao) chief scientist Dr Fernando Camilo.
Camilo is a former senior research scientist at Columbia University, in New York, US, and joined the Square Kilometre Array South Africa (SKA SA) in April 2016.
The telescope is the precursor to the larger SKA international project, which will also host some radio antennas in Australia in a project called Pathfinder. The eventual objective for the sites in South Africa and Australia is to encompass a total collecting area of about 1 km2.
MeerKAT consists of 64 antennas, or dishes, each of which has a diameter of 13.5 m. The antennas are located on baselines (distances between antenna pairs) of up to 8 km. The dishes are of a highly efficient design, with up to four cryogenic receiver systems operating in different bands of the radio spectrum. The first installed set of receivers operates between frequencies of 900 MHz and 1 670 MHz. The vast amounts of data from the dishes – up to 275 GB/s – are processed in real time by a correlator, followed by a science processor. After further offline analysis, images of the radio sky are generated.
The Karoo region, near Carnarvon, was selected as an ideal location for the South African component of SKA because it is a radio quiet region.
Radio telescopes do not require “dark skies”, such as optical, or ordinary light, telescopes, such as the South African Large Telescope, in Sutherland. Therefore, radio telescopes can be used during the day.
It is easier to look into the centre of the Milky Way galaxy from the southern hemisphere because the Milky Way is directly overhead, whereas, in the northern hemisphere, it might hug the horizon or not be visible at all.
Once complete, the SKA project is expected to be 50 times more sensitive and up to 10 000 times faster (in terms of survey speed) than the best radio telescopes currently available.
MeerKAT was inaugurated by various key government figures, including Deputy President David Mabuza, Science and Technology Minister Mmamoloko Kubayi-Ngubane and former Science and Technology Minister and current Higher Education and Training Minister Naledi Pandor.
At the launch, a panorama image created by MeerKAT – showing astronomical phenomena detail in the region surrounding the supermassive black hole at the centre of the Milky Way galaxy – was unveiled.
The centre of the galaxy was an obvious target. “One of the first things many radio astronomers want to do with a new radio telescope is point it at the centre of the Milky Way,” says Camilo, adding that the region is visually striking and full of unexplained phenomena.
The centre of the Milky Way, lying behind the constellation Sagittarius, is 25 000 light years from earth. At this distance, it would take 25 000 years for light and radio waves to travel from the central region of the Milky Way to reach the earth.
The region is impossible to observe from earth using any currently available, ordinary visible light telescope because there is too much gas and dust in between. However, Camilo says radio waves can penetrate that dust and gas, thereby providing an eye into the “core, the heart of our galaxy”.
The only other means of peering through the vast volumes of gas and dust are infrared imaging and X-rays, but radio wavelengths still trump them.
The never-seen-before panorama image was sent to a handful of overseas scientists for peer assessment and review. US-based Northwestern University physics and astronomy professor Farhad Yusef-Zadeh says the image is “remarkable”. He is an expert on the mysterious filamentary structures shown in the image that are present near the central black hole, but nowhere else in the Milky Way.
These long and narrow magnetised filaments were discovered in the 1980s using the Very Large Array (VLA) radio telescope in New Mexico, US, but their origin has remained a mystery.
“The MeerKAT image shows so many features never seen before, including compact sources associated with some of the filaments, that it could provide the key to cracking the code and solve this three-decade riddle,” says Camilo.
The design of MeerKAT was optimised in 2010 and 2011 to study hydrogen, says Camilo, pointing out that hydrogen is the simplest element and most stars and galaxies are made up of hydrogen.
“If you study the raw fuel, which is hydrogen, you can learn a lot.”
Therefore, Camilo, the Department of Science and Technology and Sarao are studying hydrogen, because, according to Camilo, a fundamental understanding of how galaxies such as the Milky Way came to exist is yet to be developed.
The universe is 14-billion years old and the earth’s galaxy (the Milky Way) is about ten-billion years old, while the solar system and earth are about five-billion years old – but things evolve, he says. The galaxies at the beginning of the history of the universe looked very different from the way they do today. “We want to study how we got to where we are today,” adds Camilo.
However, studying hydrogen many light years away is challenging. The element emits very faint radio signals at one specific frequency and at an electromagnetic spectrum of 1 420 MHz. The radio signature of hydrogen, being very faint, requires a very sensitive radio array like that of MeerKAT.
Meanwhile, in terms of studying distant radio wavelengths, MeerKAT has exceeded all expectations, says Camilo, recalling early interest in the telescope’s capabilities.
Prior to joining Sarao (and, consequently, the MeerKAT project), he received one of the first plot graphs in 2015 that illustrated the sensitivity of the first antenna installed and commissioned at the MeerKAT site. The results from one antenna astounded Camilo, who, when studying the information, thought that “something is wrong here, somebody forgot to divide by a factor of two”.
He consulted notes taken in 2009 about the MeerKAT project. “These new numbers, if true, showed that MeerKAT would be twice as sensitive as what the international community were promised in 2009. Something like this never happens. You do not build a project of this complexity and end up with something better than was initially planned.”
Even in an ideal scenario, Camilo says, it would be sheer luck to achieve what was initially planned, referring to the sensitivity of MeerKAT. The end result is often not quite as good as expected because a pioneering project like MeerKAT is leading-edge technology. Camilo comments that too many things have to work in a finely tuned manner for the whole project to work optimally.
Camilo established that the first antenna’s data and figures were, in fact, correct. “At that point, I wanted to learn more about MeerKAT . . . there was a position available, and I subsequently moved to South Africa in 2016.”
MeerKAT is a “discovery machine”, he declares.
In 2009, the SKA project made a call (observing proposals) to the international scientific community, requesting interested parties to propose large-survey projects (LSPs) comprising about 1 000 hours of telescope time per project over a five-year term.
“As far as LSPs are concerned, a thousand hours is a long time,” highlights Camilo, explaining that LSPs undertaken by the VLA radio telescope comprise about 200 hours. He adds that the VLA was the ‘gold standard’ of radio telescopes prior to the introduction of MeerKAT.
LSPs were submitted by 21 teams worldwide, after which only ten were selected, following an independent review process, for operational time on the telescope in the near future. These projects include Radio Pulsar Timing, Laduma, MeerKAT Absorption Line Survey, Mhongoose, Trapum, MeerKAT HI Survey of the Fornax Cluster, Mightee and ThunderKAT.
The Radio Pulsar Timing project will serve to test Albert Einstein’s theory of gravity and gravitational radiation, investigating the physics of enigmatic neutron stars by observing pulsars.
Laduma – Looking at the Distant Universe with the MeerKAT Array – is an ultradeep survey of neutral hydrogen gas in the early universe.
The MeerKAT Absorption Line Survey plans to study atomic hydrogen and OH lines in absorption against distant continuum sources. OH line ratios may give clues about changes in the fundamental constants in the early universe.
Mhongoose – MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters – will investigate different galaxies, dark matter and the cosmic web.
Trapum – Transients and Pulsars with MeerKAT – will search and investigate new and exotic pulsars.
The MeerKAT HI Survey of the Fornax Cluster involves looking into galaxy formation and evolution in the cluster environment.
Mightee – MeerKAT International GigaHertz Tiered Extragalactic Exploration Survey – involves deep continuum observations of the earliest radio galaxies.
ThunderKAT – The Hunt for Dynamic and Explosive Radio Transients with MeerKAT – will investigate occurrences, such as gamma ray bursts, novae and supernovae, as well as new types of transient radio sources.