Honorary Doctor of ĚÇĐÄvlogĂŰĚŇ, Professor Hans Kjeldsen: “Astrophysics Is an Actual Way to Attract the Next Generation Into Science Questions”
For almost three decades, Professor Hans Kjeldsen from Aarhus University (Denmark) has been working closely with scientists from the Faculty of Physics at ĚÇĐÄvlogĂŰĚŇ (VU), studying the composition of stars. In 2024, he was awarded an honorary doctorate from VU for his outstanding scientific achievements and long-standing partnership with Lithuanian astronomers. The asteroseismology methods he has developed allow us to look into the depths of stars through their vibrations and have been implemented even in NASA’s Kepler space mission, opening up new opportunities to understand the evolution of stars and detect exoplanets (planets orbiting other stars outside the solar system).
Asteroseismology: what the vibrations of stars reveal
Prof. H. Kjeldsen is not only one of the world’s most renowned asteroseismologists. He is well known in the scientific community as an expert with a warm and open communication style, an ability to clarify complex issues, and a sincere dedication to both research and teaching.
Asteroseismology is similar to seismology on Earth, except that instead of earthquakes, oscillations and vibrations in stars are observed. According to the astrophysicist, a telescope may show what happens in a star, and then one gets a very long extended series of data, but the whole excitement is – what does one learns and how the information is extracted.
“I have, over the years, together with a group in Aarhus and here in Lithuania, built techniques to extract that information to learn really deep things about stars. I still remember the first time I even saw these vibrations in my data. This is such an inspiring thing – you see things that no one else has seen before. The universe showing things that we need to measure and then extract the information is an enormous inspiration – you can sit there and try to make the next puzzle in the whole landscape of science,” the professor described the information hidden in the depths of stars, which cannot be seen from the outside. This includes, for example, their internal structure, physical processes and evolution.
From MolÄ—tai telescopes to NASA missions
The scientist has fond memories of his first visit to the VU MolÄ—tai Astronomical Observatory, surrounded by nature. At that time, he participated in one of the first international summer schools for students.
“It was actually a Norwegian professor, Jan-Erik Solheim, who invited me. Professor Gražina Tautvaišienė also have known him for many years. When I came there, I really liked the whole environment, having all the students using all the facilities and also having an extremely high level of ambition. Not necessarily academically, but we wanted to push the students to the limit of what we could also do. Then I met the staff here. Young and older. They were all really dedicated. As teachers, we were so close to the students and their projects that we supervised them in small groups. Because we were here in Molėtai, there was no way of escaping. In those days, you were away, you were sitting, concentrating or focusing on the whole thing. I was super inspired by this. I didn’t know how to do it in Denmark, but here it worked,” jokes the professor, recalling a time when there were no smart devices and a constant flow of information.
Prof. H. Kjeldsen recalls that soon not only the telescopes of the VU MolÄ—tai Astronomical Observatory were put into use, but also remote observations with the Nordic Optical Telescope and telescopes from other observatories. A group of scientists in Lithuania analysed stars, their atmospheres, and properties, using a lot of spectroscopy.
“In those days, I actually didn’t work a lot on exoplanets, but that came along with our collaboration with the USA and the Kepler NASA space telescope group. We also brought all of that data from the space mission into the summer schools. We developed research activities that are very aligned with other summer school activities. Research grew out of the schools, and then we figured out that if we developed a project together, the way we organise a space mission was also an open thing. We decided to have a completely open environment in the space mission so that every student and researcher could join the teams. You didn’t have to contribute financially to anything; you had to use your brain and work on the data because there was so much data. No one could cope with all that,” says the professor.
According to the researcher, measurements of individual stars, such as determining their chemical composition, age, and evolution, are carried out at the VU MolÄ—tai Astronomical Observatory and are very useful when linked to other data.
“The things were aligned, but it was not that we, with VU astrophysicists, tried to do it in parallel; we had to work together. And this is what astrophysics is so strong about,” emphasises the researcher. He greatly appreciates the expertise of the scientists working at the VU Molėtai Astronomical Observatory and the equipment available there.
“This telescope is really great, and the science that comes out of Molėtai is really producing the data that you don’t get anywhere else. Specifically because the group here also analysed the data and knew what to do. So, one thing is to get data in the beginning, but how do you understand that, and how are you sure that you understand that correctly? They have developed that for 20 years here in Vilnius, so this is also what I find fascinating – we can come here and collaborate on the data to make sure that the future space missions understand data in the correct way,” says the professor.
Collaboration in science strengthens our understanding of the universe
Prof. H. Kjeldsen mentions several reasons why international cooperation in astronomy is essential.
“One is that objects in the universe are like anything emitting electromagnetic radiation in the full spectrum, from x-rays, visible light, infrared, ultraviolet, to radio waves. To understand any object fully, you need the whole spectrum. No one has access to all instrumentation, so if you don’t collaborate, you’ll be studying only a part of the system.
It is not like in different types of physics experiments, where you have one main instrument and you work on that. We use space missions, ground-based, and the Molėtai is a great example of this. You actually can’t do what you do in Molėtai in a space mission. There is no way of doing that with any space mission. You would ask why not? Because those kinds of instruments are huge and heavy, you can’t fly them and get them to work,” the scientist highlights the importance of local resources in the context of global research.
Another important reason is that the research area is quite small. According to the honorary doctor of VU, even with all the data available, its analysis requires joint knowledge and efforts. “There are too few people; we are not the department that could do it internally. This is, of course, no problem if you establish these collaborations. It is not only Lithuania that I collaborate with; there are many other groups, although this is one of the closest connections I have because we built it up this way – the collaboration, which is essential for me to answer the questions.“
The researcher also identifies collaboration as a valuable stimulus for student improvement. The international environment encourages young people to develop their own ideas and broaden their horizons, while getting to know their colleagues and their methods becomes an integral part of their professional growth. “Of course, you can do that by knocking on the doors of my colleagues, but it is much more natural to send students here to the summer schools,” tells Prof. H. Kjeldsen.
Science – part of culture and a value-based activity
The professor sees science as a cultural thing. “Science is one thing where we could have really good discussions across cultures and languages. I think that a super important thing is to try to understand other societies, cultures, and ways of working. Through this, of course, you end up thinking, “Okay, not everything is like at my home. Science is a common interest,” and the astrophysicist emphasises the importance of openly sharing knowledge around the world.
According to him, this kind of culture of openness is particularly strong in astrophysics, which requires international infrastructure and cooperation between many countries: “It is not only about the small countries. If you go to even NASA, it’s a huge, inspiring organisation. They have worked for complete openness. Thanks to some of these big missions and big organisations – that is actually why we get all these things [data] for free. The idea that all the data should, in principle, be open for all of us.”
He also emphasises that science should not be viewed solely through an economic lens – it is, above all, a value-based activity founded on a culture of cooperation. According to him, this culture is essential in both Lithuania and Denmark if we want to maintain an open and sustainable science system.
Explanations are understandable for both a primary school student and a PhD student
Prof. H. Kjeldsen is actively involved in popularising science among the general public and strives to speak simply when teaching, applying various teaching methods. According to him, one of the most important aspects is to link what you want to teach to your own culture and language.
According to the professor, although access to information is no longer difficult today, other challenges arise that require more responsibility and critical thinking in the process of evaluating it.
“We educate teachers and researchers, and this idea is important for both. For example, like in Lithuania, we don’t speak English in daily life, and when you go to the internet, you get all these words in English. I see this in my students and the students I supervise. When they’re writing reports, they get these words, and I don’t actually know their meaning. Although it’s a simple word in a way, they try to make a Danish version of it, and sometimes I’m reading that text and say, “I’m not sure you mean what you say because this word actually has a different meaning,” the professor says.
An astrophysicist aims to communicate science as clearly as possible and “translate” specific scientific language for different audiences: “Astrophysics is an actual way to attract the next generation into science questions. I often try to simplify things, and I realise that many of the things that I use at 1st year of university I can bring into the classroom of a primary school. Of course, they’re not exactly the same, and I’m not talking about technical mathematical things. And this is why astrophysics is so good about – you can describe things. For example, the surface of another planet is easily understood; you can talk about mountains, stones, and galaxies. Often, when you have worked a lot on your own research, you tend to forget what can be understood and what cannot.” – he is convinced that this is an area where it is particularly easy to arouse curiosity and help people understand the world. His experience is no different – just before 1st grade, he found out about the first rockets being launched and people landing on the moon, and became fascinated by the sky, the stars, and the planets.
“Although I could be teaching less, I really continue with that for both because I really like it and, when I present things, I know better what I understand and what I don’t understand, and I have to explain it. And if the students in the classroom or children in primary school don’t understand what I am talking about, then it is of course me doing things incorrectly,” concludes astrophysicist, emphasising that education is an integral part of research.