Modelling a billion years of cosmic history

Newnham Fellow Dr Ricarda Beckmann aims to bring the wonders of the Universe to new audiences to share her discoveries of the role black holes play in galaxy formation.

Look up in the night sky and it is awe-inspiring to consider the billions of stars and galaxies overhead. This sense of wonder is what Dr Ricarda Beckmann aims to harness in talks at schools and events, including her well-received talk at our 2022 Festival of Arts, Science & Ideas. For though there has been great progress in increasing diversity in the field of astrophysics, with what she describes as a ‘generational shift’ in the number of young women entering the field, Ricarda is passionate about going further.

‘Newnham has a strong history in this area, and the beautiful Observatory was a symbol of intent when it was first built,’ she explains. ‘Astrophysics is a complicated subject and that can put some people off, but there are lots of great women involved now and I feel very supported. I aim to showcase what it’s like to do research and inspire others to go into this field.’

It’s a suitably ambitious project for a researcher who is comfortable grappling with some of our greatest mysteries: how did the universe evolve, and why are we here? Ricarda harnesses the latest technology to examine the link between supermassive black holes and their host galaxies across cosmic time, using supercomputer simulations to help illuminate how black holes influence the development of galaxies, and vice versa.

A black hole is a dense region of spacetime that has such strong gravitational effects that nothing, not even light, can escape. Ricarda explains, ‘Fundamentally, studying supermassive black holes is a quest for understanding why the Universe looks the way it looks. Galaxies today come in a wide range of shapes and colours. How a galaxy looks is determined by the age and distribution of stars within the galaxy, which in turn is determined by its evolution as most galaxies build up their stars over long periods of time. When a black hole at the centre of a galaxy becomes supermassive, huge amounts of energy are released which can turn off or slow down further star formation in the galaxy. I don’t think it’s an accident that our Milky Way has a particularly small, inactive black hole in comparison to similar galaxies, as otherwise we probably wouldn’t be here at all.’

Given the impossibility of running live experiments across time and huge swathes of space, Ricarda writes code to simulate a 3D model of a chunk of the universe emerging, changing variables to compare to the real universe, to test if her assumptions are right. The computers can show the effects of black hole size, distribution or timing of formation on galaxies. She explains, ‘On the one hand I think about processes which happen near and around galaxies, trying to understand what might influence the central black holes. On the other hand, I think of processes very close to the black hole, trying to understand which of them might leave a lasting echo throughout the galaxies.’

‘I essentially take all the physical processes that we think might shape the Universe and combine them into one very powerful algorithm. Then I get one of the biggest supercomputers in the UK to compute again and again how each process evolves and influences the others, until I have what looks like a billion years of cosmic history condensed into a short video. I use this crash course in cosmic history to look for individual galaxies and black holes and try to find points of meaningful influence, and am slowly piecing together the story of how and why black holes and their galaxies seem so tightly linked today.

‘In the last few years I have worked specifically on two different aspects of black holes. I have worked extensively on black hole physics that is normally too small to model directly in simulations and have shown that we need to change how we model how black holes move in galaxies, and how they grow over long periods of time.

‘On a larger scale, I particularly worked on galaxy clusters, which are huge collections of galaxies, with the space between galaxies filled with hot gas. Basic textbook physics tells
you that this gas should cool very rapidly, but that is not what we observe at all, which is a puzzle. Most galaxy clusters host very large jets in the centre, driven by the central galaxy’s supermassive black hole. The current idea is that these jets inject energy into the cluster that keep the gas hot, but we don’t really understand the details of how the energy is distributed throughout the cluster. The quest for the answer to that puzzle is ongoing.’

It is a fascinating but time-consuming process. Astrophysics is a field which requires collaboration, and patience, often starting with smaller questions that together offer incremental insights on far larger problems. That makes it all the more exciting when a breakthrough happens that can advance the whole field. The successful launch of the James Webb telescope and the first stunning images it has sent back to earth are the culmination of 30 years of research. Watching the programme from a distance, Ricarda is eagerly awaiting the anticipated images of some of the earliest days of the Universe. ‘The James Webb telescope will show us images we’ve never seen before of galaxies developing and growing and ultimately help open a window on the co-evolution of black holes that I focus on. I’m very excited about that.’

As a student of Physics at Imperial College London, Ricarda worked for a material science researcher, with a project involving computer simulation. This turned out to be a game-changer. ‘I was drawn to doing big simulations from that fun mix of complicated physics and powerful new technology. That job gave me a boost on my CV as I could show I had been involved in some research and simulations already and – as is so often the case – that led me, partially by accident, to where I am today.’

Ricarda’s career took her to Oxford for a PhD in Astrophysics, then a research position at the Institut d’Astrophysique de Paris, before coming to Newnham as the Ruth Holt Research Fellow in 2020. The problem of light pollution has always meant astrophysicists benefit from working in some spectacular locations, where dark skies can be guaranteed. Academic departments have sited their telescopes at the edge of cities. ‘In Paris the observatory where I did my research is surrounded by parks, and Cambridge’s Institute for Astronomy is on the road to St Neots. Of all the departments, Astrophysics have the best sites.’ As does the Newnham Observatory, nestled in the College gardens, of course: the perfect place to gaze up at the sky and contemplate the universe.