‘It is sometimes the case that bizarre phenomena are postulated before they are discovered or observed (like neutron stars and black holes!); or discovered before we have any theoretical understanding of what they are (like fast radio bursts!). As you can imagine, there’s a nervous challenge between the two – theory and observation. If we find unexpected behaviour, our understanding of nature can be dramatically challenged and has to adapt significantly (or our observing methods are deeply scrutinised!). And when we theorise new phenomena, we can set out to search for its evidence in the night skies. One example of a current challenge in this regard relates to new discoveries of ever more massive neutron stars.’

Thus explains Dr Marisa Geyer, a lecturer in Mathematics and Applied Mathematics at the University of Cape Town (UCT), and one of the High Energy Physics, Cosmology and Astrophysics Theory (HEPCAT) team.

She has a background in theoretical physics, and ‘since my Masters and PhD studies I have become ever more involved with astrophysics and observational Radio Astronomy. Before my return to academia, I worked as Operations Scientist at the South African Radio Astronomy Observatory (SARAO), where I got to be a part of the development of the groundbreaking MeerKAT radio telescope.’
‘Just recently, MeerKAT results published in Science magazine showed that we have found an object that is heavier than what we think neutron stars should theoretically become, and yet much lighter than most observed stellar black holes up to now. If this object is indeed a neutron star, it really stretches our current understanding of the particles and their interactions that make up a neutron star to begin with. See https://www.science.org/doi/10.1126/science.adg3005 in this regard.’

Dr Geyer says she was a latecomer to the action relating to MeerKAT in many ways, ‘having joined SARAO (then SKA SA) only at the end of 2017. And yet, I got to see so many of the grand milestones, as the final touches to make the telescope science-ready!’

She recalls: ‘I was very lucky to get a seat on the small plane that goes out to site once a week shortly after I started the job. Seeing the telescopes from the sky for the first time was very exciting. By a strange fluke, my uncle, who is a pilot, was asked to fly to the MeerKAT site that day and we were both so surprised to see each other on board!’

She adds: ‘The on-site bunker where all the MeerKAT computers are lined up also really impressed me.’

A special recollection was ‘the first time we saw “fringes” using 32 antennas. This was a massive milestone. The “fringes” are the interference patterns observed for every pair of antennas, and an important diagnostic for whether all the antenna pairs in the array are being combined successfully. I also got to see the very first pulsar observations conducted with the 32-antenna array! I spent quite a bit of time double checking that the sensitivity of the pulsar observations on MeerKAT were coming out as expected. As a pulsar researcher, these were the most exciting to me.

There was a lot to learn, especially also from an operations perspective – maintaining, operating and debugging a 64-antenna interferometer requires a large team with diverse domain expertise, attention to detail and note-taking.’

By the time she moved to UCT, the 64-antenna MeerKAT interferometer was an impressive and science hungry machine and she is proud to have been part of the team – ‘having gone from most of the observing calendar covered with mode-testing and debugging slots when I started, to successfully having conducted and observed its first rounds of open time proposal calls.’

Where it started: mentors and teachers
Talking about where her interest in science started, Dr Geyer says her dad is a theoretical physicist and her mom studied computer science and worked in the field, so ‘I was lucky to have a great exposure to sciences and a female role model in the sciences too.’ Throughout our childhood they shared their enjoyment of science with us, with dinner table discussions often leading to explanations of “how the world works”. I wasn’t pushed towards Physics or Mathematics, but the love of these sciences stuck!’

‘I also had a vibrant mathematics teacher at school, who would come into class starting an arithmetic riddle. She would say something like “three plus seven times eight minus four …” and then kept going for what felt like an eternity, until finally asking who had the answer. There were always only a few students remaining at the end. It was a fun puzzle to start the day.’

Dr Geyer also remembers meeting a special mentor: ‘During my PhD, and after having picked a pulsar research project (but still figuring out what pulsars are), I met Dame Jocelyn Bell-Burnell, the woman who had famously discovered the very first pulsar. When she introduced herself, I was so overwhelmed that all I managed to say was “I’ve heard that name somewhere before”. Of course, being Jocelyn, she was ever gracious about my blunt response, and an incredible mentor throughout my PhD work!’

More about being a scientist
For the sake of those still thinking about a career in science, Dr Geyer says: ‘Being a researcher is a highly independent pursuit, which means it comes with a lot of creative freedom, and many opportunities for you to decide for yourself what problems for example you want to focus on, who you want to work with, what research collaborations you want to be a part of, and so on. This means no year, month or day is the same. I really like this about being a scientist.’

She adds: ‘Do not underestimate the value of hard work and doing something on your own for the sake of understanding something new. It can be really satisfying to grasp something new for the first time – but often it can take many attempts to get there! Make sure you ask questions in discussions when you don’t understand something: it is important to learn from others in this way.’

A good understanding of Mathematics is the foundation of Physics and Astrophysics. ‘The HEPCAT group, led by well-known Cosmologist Prof Amanda Weltman, has many interests and focuses. Most recently the group is working on using fast radio bursts to deepen our understanding and tests of cosmology, and using pulsar timing arrays to search for and characterise the gravitational waves expected to come from a population of supermassive black holes. The group really aims to bridge between theory and observation, with experts on either side, so that the projects can propel each other.’