Congratulations Kavli Prize Winners 2022!

Jørgen Christensen-Dalsgaard, long-time Editor of Living Reviews in Solar Physics shares Kavli Prize in astrophysics

01 June 2022

The Norwegian Academy of Science and Letters has decided to award the 2022 Kavli Prize in Astrophysics to Conny Aerts, Jørgen Christensen-Dalsgaard, and Roger Ulrich. They share share the prize for their pioneering work in developing the fields of helio- and asteroseismology, and for breakthrough research that 

“has laid the foundations of solar and stellar structure theory, and revolutionized our understanding of the interiors of stars.” 

Springer Nature is honored to have been collaborating with Jørgen Christensen-Dalsgaard as one of the founding editors of the journal Living Reviews in Solar Physics, co-author – with Conny Aerts and Donald W. Kurtz – of the seminal book Asteroseismology (2010), and the recent review article "Solar structure and evolution" (2021), among many other works. Roger Ulrich has published for more than three decades in the journal Solar Physics, while both Conny Aerts and Jørgen Christensen-Dalsgaard have also contributed invited articles in The Astronomy and Astrophysics Review.

The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience – transforming our understanding of the big, the small and the complex. The Kavli Prize consists of USD $1,000,000 in each of the scientific fields.

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Citation from the Committee:

The study of observed oscillations on the Sun’s and on stellar surfaces, helioseismology and asteroseismology, couple mathematical modeling with space science technology. This study involves data-analysis methods such as time series analysis, pattern recognition, and statistical modeling, while relying on various fields of physics and chemistry such as thermodynamics, nuclear and atomic physics, and quantum mechanics. The bridging of these scientific fields, starting from the appropriate observational input, allows the extraordinarily precise determination of the physical properties of stellar interiors. Roger Ulrich led the theoretical foundation of the field, while Conny Aerts and Jørgen Christensen-Dalsgaard have extended its reach to stars of all masses in various evolutionary stages, using both ground- and space-based observations.

Roger Ulrich was the first to show that the oscillations observed on the solar surface can be used to make precise measurements of the characteristics of the interior of our nearest star. Ulrich derived the equations of helioseismology and interpreted the oscillatory surface phenomena as the surface response to interior eigenmodes. He furthermore predicted that discrete eigenfrequencies would be discovered, deriving the general behaviour of the relation between frequency (ω) and spatial wavenumber (k): To quote his original paper “…the 5-minute oscillations are acoustic waves trapped below the solar photosphere and that power in the (k,ω) diagram should be observed only along discrete lines.” Solar, and indeed stellar, oscillations contain information on stellar structure. The excellent agreement between solar calculations and observations was amongst other things a key ingredient in convincing physicists that the solar neutrino problem could only be solved by revising standard electroweak theory. Ulrich continued to lead the field with groundbreaking theoretical and observational programs over several decades.

Jørgen Christensen-Dalsgaard further developed the topic of helioseismology and played a major role in the “first generation” development of asteroseismology. Through the 1980s and 1990s, he determined the sound speed profile throughout the Sun, its 2-dimensional rotation map, its helium content, and the level of helium settling at the base of its convection zone. Christensen-Dalsgaard saw the great potential of applying this science to other stars in the Milky Way, fully realized with the launch of the CoRoT, Kepler, and TESS planet finding missions. Christensen-Dalsgaard participated actively to the preparation and exploitation of later missions. Asteroseismology gave rise to sizing, weighing and age-dating tools that have been applied to thousands of stars in the galaxy, including exoplanet hosts. Asteroseismology of cool stars revealed that the core rotation of subgiants and red giants required major fixes in the theory of angular momentum in stellar interiors.

Conny Aerts is a leading figure of the “second generation” of asteroseismology. Her remarkable involvement in observational approaches to asteroseismology, both from the ground and from space, using data from CoRoT, Kepler, and TESS, has had a very strong impact. While Christensen-Dalsgaard’s work is mainly concerned with low mass cool stars and the Sun, Aerts is widely known for her work on massive hot stars, extending the impact of asteroseismology across the Hertzsprung–Russell diagram. She is a leader in probing the interaction between pulsation, rotation, and stellar winds through an integrated approach, taking advantage of changing spectral line shapes, as well as photometric variations. In particular, she developed clever methods to identify pulsation modes in massive stars, opening the door to the modeling of their interiors. Aerts also pioneered a rigorous methodology to identify and model gravito-inertial modes in rapidly rotating stars, allowing estimates of rotation and mixing in stars with masses between 1.3 and 40 solar masses. Thus, her work has enabled the first quantitative estimates of near-core and envelope mixing, leading to significant improvements in stellar evolution theory.

Stellar astrophysics has been revolutionized by the data made available from planet hunting spacecraft – but this has only been possible given the extensive theoretical and observational groundwork done by these individuals and their collaborators.

Finally, Conny Aerts, Jørgen Christensen-Dalsgaard, and Roger Ulrich have also spent vast amounts of energy training and inspiring the next generations of helio- and asteroseismologists. All three will undoubtedly be remembered as founders of this extraordinarily effective tool that has transformed our understanding of stellar structure and evolution.