Astrophysicists believed until recently that black holes always orbited each other in circular paths while emitting energy-rich gravitational waves. The prevailing hypothesis was that they circled around each other and merged once they had lost enough energy.

Assistant Professor of Astrophysics Johan Samsing from the Niels Bohr Institute, University of Copenhagen (UCPH) has now demonstrated, however, that this is not the case: Black holes often orbit each other in eccentric paths.

It may sound like a minor detail: Is the orbit circular or eccentric? But this question makes a huge difference when researchers want to understand more about the lives of black holes and how they dance around each other.

Since 2016, astrophysicists have only been able to determine black holes’ mass and the way they spin on their own axes. To do this, they have used LIGO, an instrument capable of measuring gravitational waves emitted by colliding black holes. But with new knowledge about black holes’ eccentric orbits researchers can now gain a deeper insight into their evolution.

If black holes have followed a specific eccentric orbit, they can reveal many things: the kind of universe they have previously existed in, the forces that have influenced them (perhaps a massive gas cloud), or whether a third black hole has intervened and pushed the two black holes (a three-body problem). This latter phenomenon is now established science — partly thanks to Johan Samsing.

»Much of my work is theoretical, but the documentation is now at a level where none of the theory will change in five years,« he says.

Johan Samsing was awarded the prestigious MERAC Prize on 18 March for his research on black holes in the universe and the gravitational waves they produce when they collide.

The MERAC Prize is awarded every two years by one of the world’s largest astrophysics organisations, the European Astronomical Society. It is considered one of the most prestigious awards dedicated to young researchers in the field of astrophysics, to which Johan Samsing has devoted his scientific career.

Fortunately, he has a talent for staying focused.

»I received the prize because, for more than ten years, I have continued to ask myself the question: How can we learn more about black holes from the orbits they had before they collided?« he says.

Johan Samsing was one of the first in the world to explore this topic in depth. When he started publishing papers on the subject in 2014, he estimates that only four or five other astrophysicists worldwide were conducting research in the same area.

Today, he estimates that a few hundred astrophysicists are now studying the same phenomenon, a rise that may be linked to the ability to measure gravitational waves using LIGO, which became possible ten years ago.

As part of receiving the MERAC Prize, Johan Samsing will be one of the keynote speakers at this summer’s European Astronomical Society meeting, attended by several hundred researchers. Along with the honour, the prize includes EUR 25,000 and improved access to research funding for his future work.

Johan Samsing quite literally brings his work home with him to his house in Birkerød, north of Copenhagen. Here, his wife Akiko and their two children Kohana and Kaito, as well as visiting friends and colleagues, can gaze up at the starry sky from their living room.

The family has a dome on their rooftop for a space telescope.

»We always hope for good weather because the dome is a bit leaky, so when it rains, it drips onto the living room floor,« says Johan Samsing.

In addition, he is the creator and driving force behind a series of videos in the broadcast series Conversations at Niels Bohr’s Office, where top international researchers talk about their work.

Finally, Johan Samsing’s passion for communicating research on black holes led him to create the exhibition The Art of Space Time on the central Copenhagen square Kongens Nytorv in 2024.

Johan Samsing made headlines worldwide when he wrote about how black holes behave inside a massive gas cloud.

And as early as 2018, Johan Samsing was the first to publish a major article on the possible long-term dynamic evolution of black holes.