For his research, which focuses on the specific radiation of neutron stars, he met Professor Maurizio Falanga in Bern, and also experienced the unusual atmosphere of the Swiss capital. The enthusiastic student recounts his experiences in this article.

Meeting with renowned professor

The main purpose of the stay of Mgr. René Šprni in Bern from 29th September to 9th October 2024 was his collaboration with Prof. Dr. Maurizio Falanga on a scientific paper they are preparing together. The paper is focused on the study of a specific part of the observed X-rays from the accreting matter surrounding the remnants of stars after supernova explosions, technically known as accreting neutron stars. This is also the topic that Šprňa is addressing in his PhD thesis. "Our research is quite extensive, so we also discussed the possibility of submitting a project that would allow me to do a one-year internship at ISSI, where Professor Falanga is the director," says the astrophysics student of his visit to Bern.

In the world of neutron stars

As already mentioned, the dissertation of Mgr. René Šprni is focused on accreting neutron stars. These extremely dense stars, consisting mostly of neutrons, normally have very strong magnetic fields. They often exist in binary star systems where they orbit together with another star, for example in the case of low-mass X-ray systems this companion is a dwarf star. The enormous gravitational pull of the neutron star then attracts material from its stellar partner, which gradually forms an accretion disk around it - a rotating disk of gas and dust that heats up in the middle and emits energy, often in the form of X-rays.

Neutron stars are extremely compact, so they are very small relative to their mass. For example, a neutron star weighing as much as our Sun would have a radius of about 20 km.

Iron radiation as a key

Due to their compactness, phenomena that Einstein's general relativity helps to understand take place around neutron stars. "My work focuses on theoretical research on specific radiation in accretion disks around neutron stars. These disks contain iron, whose trace is very prominent in the observed X-rays, where it appears as a bright glowing line. From its shape - influenced by the high velocities of matter in the accretion disk - we can easily determine, for example, the inclination of the disk with respect to the observer or the position of the inner edge of the disk," explains René Šprňa the importance of observing iron emission around neutron stars.

But that's not all. In collaboration with Professor Falanga, the student manages to unravel even more. "Most theoretical models assume that the iron line in the spectrum of neutron stars comes only from the innermost parts of the accretion disk, which are most strongly irradiated by the neutron star's own atmosphere. But if the magnetic field of such a star is weaker, as is the case for many low-mass X-ray binaries, material from the disk overflows to the surface of the neutron star itself - and it is likely that some of the iron line radiation comes from there. And it is this fact that we are taking into account in our joint project, which aims to create a completely new and significantly more comprehensive view of the properties of accretion disks around these still understudied cosmic objects," says René Šprňa, describing the aim of his work.

Important advances in research

"During my stay in Bern, Professor Falanga and I made significant progress on a paper that will be one of the key outputs of my PhD studies," explains René Šprňa, the main contribution of his visit to Bern. "Professor Spranz shared with me advice on how to approach a scientific career, what is important when writing a well-cited article and what to really focus on. His support and motivation were very inspiring, and gave me energy. I also greatly appreciated his generosity and approach. The knowledge and experience I gained gave me motivation and a vision of where to take my research next."

Inspiring ISSI environment

For René Šprnja, his stay at the International Space Science Institute (ISSI) in Bern was truly inspiring. "Every day I worked in the visitor's office at ISSI, where I could concentrate on working on my paper and developing my ideas with Professor Falanga. I also met regularly with ISSI staff for lunch each day during my lunch break, which allowed me to engage in discussions on a variety of topics, not just astrophysics. I found the discussions on healthy living, other scientific disciplines or even the way waste is sorted in Bern, which is also a topic to be inspired in progressive Switzerland, inspiring. Thanks to all this, I also got a lot of practice in communicating in English. Last but not least, I also made contacts with two students from Egypt doing similar research to mine, which can definitely come in handy in the future," says the student praising his stay at ISSI.

Atmosphere in Bern

For René Šprnja, the experience in Bern was complex. "Outside the work part, I enjoyed the atmosphere of the city and the cultural differences. This experience has confirmed that I could imagine spending a longer period here and further developing my research in the inspiring environment of ISSI," explains the student. Bern, he says, offered him the opportunity to experience Swiss culture and everyday life in one of Europe's most interesting cities. He was really impressed by the city, which he describes with enthusiasm: "I explored the city during one weekend and although I have visited Bern before, I feel that this time I liked it the most. I noticed little things, like the fact that the locals walk faster than here. I think this probably has something to do with their healthier lifestyle and frequent exercise, for example the cycling system is very well integrated."

Recommendations for other students

For Mgr. René Šprnja, a PhD student at the Institute of Physics in Opava, it was clearly an extremely beneficial trip abroad. He therefore recommends this experience to other PhD students who are still considering a similar experience. "This placement was very enriching for me and I would definitely recommend it to other students. Experiences like this motivate you, allow you to make international contacts and look at your research from a new perspective," concludes the student.

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Mgr. René Šprňa

Mgr. Petr Horálek