4.9.2025
Since July, Max Grönke has officially been at the Astronomisches Rechen-Institut (ARI), and in October he and his family will move from Munich to Heidelberg. For him, it’s the astro hub in Germany – and a great opportunity, both professionally and personally. He brings not only his expertise in theoretical astrophysics but also an ERC Starting Grant on Resolving the Multiscale, Multiphase Universe (ReMMU), with which he is building his new group.
Grönke studies how gas and plasma behave in the universe. Although most of the universe is made of dark matter – roughly three quarters of all matter – modelling it is, ironically, relatively straightforward. In astrophysics, we still don’t know what dark matter actually is, but in simulations its only relevant interaction is through gravity. That makes the equations simpler, and it’s why there are huge “dark-matter-only” simulations.
Baryonic matter, by contrast, consists of mostly hydrogen and helium – seemingly simple ingredients – yet their interactions are far more complex. The physics quickly ventures into plasma dynamics, with phenomena that even the most advanced simulations can’t fully resolve. One of the main challenges: baryonic gas spans extreme conditions, from 10 Kelvin to 100 million Kelvin, often right next to each other, and with vastly different densities. It’s like having stones flying through air – the temperature and density differences create very different timescales and physical regimes, which makes accurate simulations on even the most powerful supercomputers extremely challenging.
To tackle this, he draws on methods from engineering, a field that has spent decades studying complex flows such as water and air, or water and oil. As Grönke explains, they are a theoretical group and often work things out on paper first – before checking in simple simulations whether it holds up. His focus also turns to observations: in radiative transfer simulations, he calculates how gas would appear in telescope images – because everything we see of the universe is ultimately electromagnetic radiation. The “reality check” against observational data is indispensable for him.
At Max’s table, people with widely different interests sit together, each bringing their own expertise. In the past, you might just write down a few equations, type some code, run it – and you were done. Today, ideas come from a variety of fields – mathematics, computer science, but also disciplines like engineering or the life sciences. Sometimes it’s even an obscure library that proves unexpectedly useful – this diversity makes the work not only more effective but also more lively.
One unforgettable “aha” moment came from a simulation by one of his PhD students: a wall of extremely dense gas next to a “window” with no gas at all – intuitively, radiation should pass through the window. But most of the light went through the wall. At first, he thought it was a mistake, until it became clear: the photons scattered so many times that they eventually changed frequency – and suddenly could pass through. “I was completely wrong – and it’s exactly these kinds of surprises that make research exciting.”
The move also means more exchange and collaboration. In Garching, he was a bit off the beaten path; now, he’s right in the middle of Neuenheim, surrounded by students, city life, and colleagues from many disciplines. “When you take ideas or methods from other fields and adapt them to your own research, you can make big leaps – and for that, Heidelberg is perfect.”
When asked what innovative research needs, he doesn’t hesitate: “A long-term perspective.” Time and planning security are essential to pursue bold ideas, test new methods, and let projects grow. Five years, like in an ERC grant, is a good start – but if you want to break entirely new ground, you often need more room to maneuver. That’s exactly what he associates with Heidelberg and the ARI: the chance to develop ideas over many years, build strong collaborations, and carry out research with genuine long-term vision.
On a personal level, the move is also a win: Grönke knows Heidelberg from his childhood, and the whole family will find a fitting new home here. Childcare plays an important role – his kids are used to playing with the institute’s Playmobil rockets at the Munich MPI during meetings, sometimes pretending to be space researchers just like their dad. In terms of Playmobil, the ARI might have to catch up, but he was nonetheless deeply impressed by the warm welcome: “In theoretical physics, it’s often impersonal: you arrive, here’s your key – and that’s it. At the ARI, it was completely different, and that really meant a lot to me.”
The faculty joins in: Welcome to Heidelberg, Max Grönke and team!
More information about Max Grönke and his research can be found on the ARI website
MAX GRÖNKE
