It was as if astronomers worldwide had previously only had eyes and suddenly also had ears: they developed technology that enabled them to observe gravitational waves for the first time in 2015. These are the waves that Albert Einstein predicted in his theory of relativity in 1916. These waves are all around us, but they are very weak and we can only detect them in extreme cases, such as when black holes or neutron stars collide. ‘This breakthrough is comparable to when people first detected X-rays or radio waves. That discovery allowed us to see more types of light. Still, gravitational waves are a completely new way of observing the universe,’ says Lieke van Son, assistant professor of Astrophysics at Radboud University.
The comparison with sound waves is apt because gravitational waves bend space-time at a frequency that falls within the range of human hearing. You can't just hear it when you step outside and prick up your ears. "It requires very sensitive detectors: we try to see whether the 4 km long arms of the detector become 1/1000th the radius of a hydrogen atom larger or smaller. Nevertheless, we have succeeded in recording the vibrations of colliding black holes. Translated into audio, it sounds like a chirp." Gravitational waves are observed by a global network with the LIGO observatory, located in the United States, Vigo in Italy and Kagra in Japan.
Live fast, die young
The data from the LIGO detectors are also an important source of information for Van Son. She studies the behaviour of massive stars. The life cycle of these stars can be summarised with the motto “Live fast, die young”. "They shine the brightest, burn the most fuel and, when their time comes, these stars explode. What remains is a black hole or a neutron star."
To study the behaviour of massive stars, Van Son uses models that simulate their evolution. She then compares these simulations with data that LIGO releases every few years. Piece by piece, she is gaining a better understanding of how the universe works. At the same time, every new insight makes her realise how much there is still to discover. "We know that we actually understand very little about massive stars, but that only makes it more fun."
Chemical factories
Over the past decade, astronomers have confirmed that almost all massive stars live in pairs, triples or even quadruples. "These stars interact with each other: they orbit each other and exchange mass. We still know very little about these interactions and, in fact, about the life and death of massive binary stars." And yet it is precisely these stars that have had a major influence on the formation of our universe through their emissions. "Massive binary stars are the chemical factories of the universe. Elements such as oxygen, carbon and gold originate from these stars."
In the coming years, Van Son will specifically examine how massive stars exchange mass with each other. "We distinguish between stable and unstable transfer," Van Son explains. "In stable transfer, one star gradually transfers mass to the other. In unstable transfers, one star gives away more and more mass until one star engulfs the other."
Disastrous cutbacks
It comes as no surprise that Van Son studies the universe as a scientist. Even as a child, she asked big questions: “Where do we come from? How did our universe come into being?” Although she had doubts in secondary school about whether studying astronomy would be too difficult, she went for it. "It actually went very well and I really enjoyed the course. My drive and interest only grew."
Although the past ten years have been one big success story and a great deal of groundbreaking research has taken place since the first observation of gravitational waves, cuts to science funding are also threatening astronomy. In the Netherlands, cuts to higher education are having a severe impact on research. "But also in America, Trump proposed cuts that would lead to the closure of one of the LIGO detectors. That would ruin all the progress in the coming years.’ Van Son believes that research into these kinds of fundamental questions can have a unifying effect. ‘When it comes to the question “where do we come from”, every human being feels a certain curiosity and wonder."
Want to stargaze yourself?
There are regular stargazing evenings on campus. Accompanied by volunteers from the Astronomical Circle Nijmegen, you will be given a guided tour including stargazing (weather permitting), a lecture by an astronomer and a Q&A panel in which astronomers discuss recent astronomy news and answer questions.
The next stargazing evening is on Friday 31 October. More information