Biermann Lectures 2025: Diving deep into the stars with asteroseismology
By Prof. Conny Aerts, KU Leuven, Belgium
Different musical instruments make different characteristic sounds, as a consequence of their different structures. An orchestra has diversity in brass and percussion, woodwind and strings, not for the visual variety but because the different instruments make different musical tones and melodic colours: a cello can make different sounds from a violin, and a tuba different sounds from a piccolo. Now imagine only hearing a new musical instrument, and having to work out the construction of the instrument from details in the sound waves.
Seismologists do something similar with the Earth itself, from listening to seismic waves travelling through the Earth with careful instruments to gain information about the internal structure of our home planet. Asteroseismologists use the same principle to infer the internal structures of stars. We cannot hear sound waves from the stars, of course, since they do not reach us through the vacuum of space. Yet carefully observing the light from stars can indicate how they are oscillating, and so allow us to infer how waves travel inside those stars. In turn, combining detailed observations and models teaches about the structures inside stars. This method for investigating the interiors of stars has been used for several decades on the nearest example – our own Sun – but we were unable to adequately measure the oscillations of more distant stars.
Conny Aerts has been a leading figure in turning asteroseismology into a field which now gives insight into diverse stars beyond the Sun. With a background in mathematics, Conny and her group have developed powerful methods to interpret asteroseismic signals. Conny has further applied these techniques to data from satellite telescopes – notably NASA’s planet-hunting missions Kepler and TESS – to reveal new information about the insides of a broad range of stars.
Conny is well-known for developing asteroseismology to make discoveries about the internal structures of stars significantly more massive than the Sun. When converting hydrogen to helium in their centres, such massive stars develop convective cores. Understanding the transition from highly-turbulent convection in the core to a stably-layered envelope has defeated even the most sophisticated simulations so far. Conny’s group has led in using asteroseismology to probe the deep interior structures of these massive stars, moving us towards resolving this long-standing uncertainty in stellar physics.
Another prominent example of the leadership from Conny’s group, based on the methods she has developed, is in making measurements of the internal rotation of stars. This involved moving past a perturbative approach to treating rotational effects, and also beyond using spherical harmonics to represent the oscillation modes. Conny’s work has thereby led to insights into angular-momentum transport inside stars, and also to constraining the mixing associated with this rotation.
Conny’s fantastic scientific work has won an extraordinary number of prestigious awards. The citation for the 2022 Kavli Prize in Astrophysics, to Conny Aerts and her co-laureates, was: “for their pioneering work and leadership in the development of helioseismology and asteroseismology. Their research has laid the foundations of solar and stellar structure theory, and revolutionized our understanding of the interiors of stars.” She also won both the Francqui Prize for Exact Sciences and the 5-year FWO Excellence Award for Exact Sciences (in 2012 and 2020, respectively), and in each case was the first woman to receive them since their creation. In 2023, Conny was made a Grand Officer in the Order of Leopold, the highest Belgian order of merit, and in 2024, she recieved the acclaimed Crafoord Prize in Astronomy.
Conny is the Belgian principal investigator for the European Space Agency’s PLATO satellite, due to be launched in 2026, which promises to be even more powerful in enabling asteroseismology of massive stars. She continues to serve on the Editorial Board of the Annual Review of Astronomy and Astrophysics, and was a member of the “High Level Expert Group” on the interim evaluation of the Horizon Europe program. Conny is one of the rare scientists in Europe who has been awarded two Advanced Grants from the European Research Council, and is currently leading the ambitious ERC Synergy grant “4D-STAR”.
In her Biermann lectures this year, Conny Aerts will talk about the observational aspects of asteroseismology, the theory behind it, and how to combine both to study the insides of stars – learning more about their interior structures, and the physics which operates during their evolution.
Overall title: Diving deep into the stars with asteroseismology
All lectures take place in the MPA Large Seminar Room E.0.11
Wednesday, 8th October 15:30
Basics & applications to high-frequency waves in "sun-like" oscillators
Wednesday, 15th October 15:30
Applications to low-frequency waves in fast-rotating stars
Wednesday, 22th October 15:30
Intermediate- & high-mass stars with waves beyond a perturbative approach
