When South Africa’s MeerKAT radio telescope was switched on in 2018, it cemented itself as one of the world’s most powerful astronomical instruments, capable of uncovering deep cosmic mysteries. Behind its success is a network of engineers and astronomers who worked tirelessly to fine-tune its performance. Among them is Dr Benjamin Hugo, a key player in the commissioning and science verification of MeerKAT and one of the country’s leading experts on its use.
Dr Hugo is a staff astronomer with the South African Radio Astronomy Observatory (SARAO) in Cape Town. He completed his PhD at Rhodes University and it examined the commissioning, characterisation and science verification of the MeerKAT radio interferometer. He played an essential role in ensuring that the telescope met its ambitious design specifications and his research has been pivotal in improving calibration techniques and broadening understanding of the not-yet well-understood class of transitional pulsar systems.
Radio telescopes like MeerKAT are intricate systems made up of large antenna dishes, powerful receivers and cutting-edge digital processors. But before they can reveal the secrets of the cosmos, they must be meticulously tested, calibrated and refined. This is where Dr Hugo’s work came in.
“Radio telescopes, like the MeerKAT telescope near Carnarvon in the Northern Cape, are complex instruments that involve many disciplines: from mechanical and structural engineering to ensure the antennas (dishes in the case of MeerKAT) accurately point where you tell them to, through a complex digitisation process which takes the analogue voltages from individual antennas to combine them with other antennas using specialised programmable hardware,” he explains.
“Many things can go wrong in this complex chain, so before any science can be done, it is critical to ensure that the instrument meets its design specifications, trace down issues and understand any particular quirks of the instrumentation and the environment. This is what commissioning entails.”
As part of the commissioning team, Dr Hugo helped test MeerKAT’s antennas, refined how the telescope processes signals and developed strategies to correct for interference. His research revealed that MeerKAT was so sensitive that traditional calibration methods fell short. To solve this, he studied how background radio signals influenced the telescope’s accuracy, ensuring that faint cosmic signals do not have a negative effect on calibration.
“Very early on during the commissioning process we found that MeerKAT was so sensitive that the calibration procedures typically followed were inadequate. I characterised the population of radio sources surrounding our main calibrator fields to reduce their influence on the frequency response of the instrument.”
A key breakthrough involved studying the Moon’s natural radio emissions.
“The receiver of a radio telescope acts similar to a pair of sunglasses. Each MeerKAT dish has multiple receivers sensitive to a small piece of bandwidth, each in-turn has a vertical and horizontal open wire (a 'dipole' antenna – think of your grandmother's old rabbit ear antenna on top of her TV) that is sensitive to either the vertical or horizontal component of radio light. Each acts as a set of sunglasses with vertical or horizontal slits blocking out horizontal or vertical light.”
By analysing how the Moon, Venus and Mars interacted with MeerKAT’s receivers, Dr Hugo was able to refine the telescope’s ability to measure the polarisation of cosmic radio waves – an essential tool for understanding the structure and magnetic fields of distant galaxies.
Unlocking the secrets of pulsars
Beyond calibration, Dr Hugo’s research took him into the realm of pulsars; these are spinning neutron stars that act like cosmic lighthouses, flashing beams of radiation as they rotate. His work focused on a rare type of pulsar that shifts between two different states, alternately emitting radio and X-ray signals.
“Pulsars are neutron stars that have very fast and stable rotational periods – most ranging from milliseconds to a few seconds. They very slowly lose their kinetic energy through the radiation emanating from their poles, which we see as pulses of radio light as the poles intersect our line of sight to these stars,” Dr Hugo says.
“These neutron stars are often spun up (or were spun up in the past) by a companion star, which they slowly strip material and gasses from. When this accreted material falls onto the surface of the neutron stars, thermal reactions are seen in the X-ray spectrum, accompanied by the pulsed radio emission turning off and being replaced with continuously emitting radio emission.”
Using MeerKAT and the space-based XMM-Newton X-ray observatory, Dr Hugo identified a candidate system where a pulsar was actively pulling in matter from a companion star, offering a rare glimpse into a poorly understood astrophysical process.
“This transitional mechanism between a neutron star accreting material and starting to pulse is not well understood because the observational timespans needed to detect such traditional systems are measured in decades. I detected a potential such candidate in the radio for the first time as the system is actively accreting material from its companion (as seen in optical and X-ray observations).”
Making sense of Big Data
MeerKAT doesn’t just capture spectacular images, it generates vast amounts of data, with individual observations reaching hundreds of terabytes. Managing and storing this information is a major challenge. Dr Hugo’s research tested ways to compress these data sets by an order of magnitude while preserving their scientific integrity.
“MeerKAT data products are often hundreds to thousands of gigabytes (GBs) in size after calibration (and even larger before calibration). This poses a substantial and costly problem for keeping this data long-term for the sake of further analysis and scientific reproducibility. We show that we can compress calibrated MeerKAT products by at least an order of magnitude without compromising the integrity of these products.”
This breakthrough is particularly important as South Africa prepares for the next phase of the Square Kilometre Array (SKA), an international mega-project that will be the world’s largest radio telescope.