Interview with Johannes Geiss Fellow Bruno Leibundgut

Bruno Leibundgut (European Southern Observatory (ESO), Garching, Germany) was elected as the Johannes Geiss Fellow 2019. He will give a Pro ISSI Talk on “Cosmology Today”, October 14, 18:15h CET. You can join this talk online (Zoom Webinar): https://bit.ly/2DJ74Pr  Meeting ID: 81330166057 Password: 481628. More Information about the Pro ISSI Talk >>

In the following paragraphs he answers a few questions – asked by Lorena Moreira, ISSI Earth Sciences Post Doc – about his scientific work (in pandemic times).

Lorena Moreira: How has the Johannes Geiss Fellowship contributed to your career? And why did you apply to the Fellowship?

Bruno Leibundgut: The Johannes Geiss Fellowship was a great opportunity for me to refocus some of my research and reconnect to Swiss astronomy. Most of my professional career was spent at an international organisation and an observatory. This means that I had to deal with many science administration aspects and for a while, during my time as ESO Director for Science, was contributing to the scientific direction of the organisation and managing the scientific environment. There was not much time left for research. 
The Johannes Geiss Fellowship allowed me to catch up with recent developments in my fields of supernova physics and cosmology. Being able to devote all of my time to research was a very welcome change to my current work. This was also the reason to apply for the Johannes Geiss Fellowship. It seemed to be an ideal opportunity to combine the research time it promised at a scientific institute in Switzerland. I used the time to meet several astronomers in Bern and Geneva to discuss various projects and the interaction of Swiss astronomers with ESO.

 

Lorena Moreira: On which projects did you work during your stay at ISSI?

Bruno Leibundgut: The original plan was to write up a paper from a Masters thesis of one of my students on SN1987A. He analysed the evolution of this nearest supernova in several centuries from a decade of HST observations and his results should be cast into a publication. My first weeks at ISSI were used to clear my ESO work backlog. I also had a couple of trips to conferences and for talks during my Johannes Geiss Fellowship. My research at ISSI focussed is on some cosmology aspects, which I wanted to explore more deeply. This also involved learning new software tools. The time at ISSI enabled me to enlarge my knowledge and read up on topics, which in my normal work life always seemed to fall to the wayside. 
The main research work in the end was on the adH0cc (accurate distances for H0 through core collapse supernovae) project. I am leading a large programme with the ESO Very Large Telescope (VLT) to carefully observe about 2 dozen individual Type II supernovae to determine their distances and then derive the local cosmic expansion rate, the Hubble constant. We acquire detailed spectroscopy and photometry of a supernova over several weeks to follow its brightness evolution and the speed with which it expands to connect these parameters into a distance measurement. Much of the data reduction processes were worked out during my time in Bern.

Lorena Moreira: What are according to you the next breakthroughs in cosmology? What do you think the future hold for your scientific career?

Bruno Leibundgut: There is a discrepancy of the value of the Hubble constant from measurements in the local and the distant universe. This ‘Hubble tension’ could, if confirmed, point to deficiencies in the currently favoured cosmological model, the Lambda Cold Dark Matter (Lambda CDM) universe. This model contains several components that at the moment lack a physical understanding, namely ‘dark energy’ in the form of Einstein’s cosmological constant Lambda and ‘dark matter’, which is inferred indirectly, but has so far not been detected as a particle. These particles would have to be fairly massive so that they can clump under gravity to form galaxies. We call this type of matter ‘cold’. The difference of the Hubble constant as calculated from the information in the distant universe, the measurements from the cosmic microwave background as determined by the ESA Planck satellite, and the direct measurement in the local universe shows that the Lambda CDM model may not be complete. Right now it is unclear, whether this is a real physical effect or just systematic problems of the Hubble constant determinations. It is important to explore as many independent methods as possible to check that we are not fooled by unknown problems in the measurements. 
Our adH0cc project contributes a new method of the local Hubble constant that is completely independent of any of the other determinations. It will take a couple of years until we have collected the necessary data and can analyse them. In the end, we should be able to check for any systematic effects we use to measure the Hubble constant. In some sense, this work arches back to the start of my scientific career, where I also tried to determine the Hubble constant – with an uncertainty that was a factor 10 higher than today’s measurements! 
I was always interested in the physics of stellar explosions and how this connects to their use as cosmological distance indicators. My research of this connection continues and I hope that I can learn about the explosion physics as much as about cosmology. There are plenty of unsolved problems in both areas. The current cosmological picture has firmed up significantly over the past two decades, but with dark energy and dark matter contains at least two parameters, which lack a physical understanding. 

Lorena Moreira: As you have recently experienced staying away from your permanent office during your visits at ISSI and during the current pandemic situation, what do you think that we can learn from these experiences to thrive scientifically?

Bruno Leibundgut: ISSI was a great place for me to focus on my research. The quiet environment allowed me to concentrate on the adH0cc project and make the necessary preparations to fully explore the data. Such quiet periods, when the hectic of the outside world is shielded, are important in a research career. I believe, they are needed to focus one’s mind. Small ’sabbatical’ stays, like my Johannes Geiss Fellowship at ISSI, are important to reflect on the research direction. The ISSI setting was especially joyful for me; I could quietly sit in my office and work for myself but was connected to the scientific environment of the institute and the University of Bern. I participated in the CSH Science and Religion Forum: “Limits of Science – Opportunities for Religion?”, which I would not have been able to do in my regular work environment, simply because there would not have been the time. The combination of ‘quiet time’ in a lively environment seems to me conducive – maybe even central – to research work. The exchange beyond the limited scientific topics to enlarge the intellectual horizons is key for good science.  
With the pandemic and increased home office the nature of meetings has changed. The many online meetings and conferences offer new opportunities, e.g. participation from different time zones and recording of presentations for asynchronous viewing. We experience an increased participation through the online format, which means that more people can attend online meetings and at a decreased cost. My experience, though, is that discussions are stifled through the online format and are much reduced. 

The future will see a combination of the different formats. Small focussed meetings to discuss specifics and with free-format discussion rounds profit from direct and extended interaction, while the general information exchange meetings should become hybrids with some physical participation and streaming/recording for a wider audience.