Kavli prize 2022 honors stellar insights
Three researchers received the prestigious prize for their breakthrough research in Astrophysics in Oslo 6th of September.
Conny Aerts, Jørgen Christensen-Dalsgaard and Roger Ulrich received the Kavli prize in Oslo Concert Hall from His Majesty The King. The prize winners have contributed with major breakthroughs in stellar physics. - They have been instrumental in giving us insight into the “unobservable” interior of stars. The prize is not just for the laureates, but for the achievement of a whole field of scientists and engineers, says Bo Andersen, former director of the Norwegian Space Agency. Photo: The Kavliprize
Roger Ulrich (USA), Jørgen Christensen-Dalsgaard (Denmark) and Conny Aerts (Belgium) received the Kavli Prize in Astrophysics 2022 for "research that has laid the foundations of solar and stellar structure theory, and revolutionized our understanding of the interiors of stars.” This includes being able to understand the inside of our closest star - the Sun.
Solar scientists at RoCS - Rosseland Centre for Solar Physics at UiO celebrates the award and director Mats Carlsson says:
It is pretty amazing that helioseismology and astroseismology makes it possible to "see" the interior of stars - what we can not get information about directly via light.
Development of new theories
The well known English astronomer Sir Arthur Eddington (1882 - 1944) was the first to make models of stellar interiors.
He is alleged to have stated that unfortunately one would never be able to observe the interiors of the Sun and other stars.
New field gives new insight
In the 1960s solar physicists observed oscillations of about five minutes in Doppler measurements of the solar surface. The Kavli Prize winner Roger Ulrich calculated that these observations could be the result of global acoustic oscillations. He furthermore predicted that there would be a large number of specific modes penetrating the interior of the Sun.
These predictions were confirmed quite rapidly by several observers where Franz Ludwig Deubner was the first in 1975. Several astronomers understood that these global acoustic observations could directly probe the interior of the Sun. In this sense, the new field of Helioseismology was a means to observe the physics and dynamics of the solar interior.
However, to be able to test what kind of interior structure the Sun has to reproduce the observations, it was necessary to have accurate models of the Sun. Several scientists developed these models in parallel, and soon the so-called "Model S" of the Kavli Prize winner Jørgen Christensen-Dalsgaard, became the reference model in 1996.
Scientists in several countries made coordinated ground based observation networks. Later space observatories on SOHO (Solar and Heliospheric Observatory) and SDO (Solar Dynamic Observatory) developed the quality of the observations.
The combination of models and observations made it clear that the previous understanding of the solar interior was wrong.
Inside the Sun
The new results showed that the outer convection zone went to a depth of 30% of the solar radius, the differential surface rotation (the equator of the sun rotates faster the closer to the poles, this is possible because the the Sun is gaeous) continued through the convection zone and was nearly rigid below that.
Furthermore, the observed magnetic field of the Sun is mainly generated by a shear dynamo effect in the transition between the solar convection zone and the radiative stable interior below. This shear in rotation speed is there because the convection zone has a differential rotation like the surface while deeper in the Sun the rotation is rigid, that is the same rotation rate independent of latitude.
The solar neutrino problem
However, the most fundamental physics discovery was that the temperature of the core was such that the observed lack of neutrinos from the Sun had to be explained by other means. The “neutrino problem” lead to the discovery of the oscillations of different type of neutrinos. The discrepancy was first observed in the mid-1960s and was resolved around 2002.
The Sun and sun-like stars constitute the majority of stars and to get observational information about the interior of these stars it would require observations of higher accuracy than was achievable.
New measurements of very small Doppler shifts of a few stars from the ground showed that these observations were possible and they confirmed the existence of stellar oscillations similar to what was observed on the Sun.
Getting to know thousands of stars
These ground based Doppler observations were tedious and it was clear that space observations of minute variations in intensity would be required. Fortunately, at the same time the quest for extra solar planets was initiated, this required the same type of accurate measurements. The launch of satellite missions like CoRoT (2006), Kepler (2009) and TESS (2018) gave the scientists a wealth of new observations that could provide knowledge of all types of stellar interiors.
The Kavli Prize winner Conny Aerts was central in using these observations to create detailed knowledge about the physics of the interiors of tens of thousand stars. She has moved the knowledge front the other Kavli laureates have contributed to on the Sun to encompass large stellar populations.
A combination of fields
Pairing the study of oscillations on the sun’s and other stellar surfaces with mathematical modeling, the laureates combined data-analysis methods (such as time series analysis, pattern recognition, and statistical modeling) with the physics and chemistry of thermodynamics, nuclear and atomic physics, and quantum mechanics. The bridging of these scientific fields allows the extraordinarily precise determination of the physical properties of stellar interiors.
All three Kavli prize winners figured out a way to look at the inside of different types of stars and developed tools to study them precisely
says Viggo Hansteen, Chair of the 2022 Kavli Prize Astrophysics Committee and professor at RoCS - Rosseland Centre for Solar Physics at UiO.
The Kavli Prize
The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience and the prize consists of USD $1,000,000 in each of the scientific field. The Kavli Prize Award is presided over by His Majesty King Harald Ceremony and was held at the Oslo Concert Hall.