A protest sign behind Floor Broekgaarden reveals her engagement: she regularly demonstrates on campus. This is in response to the Trump administration’s policy to cut funding for universities that refuse to abandon their diversity initiatives – for Broekgaarden’s university, the University of California, San Diego (UCSD), half of its budget is at risk.
Ever since Broekgaarden (1994) pulled a Stephen Hawking book from her father’s shelf at age fifteen, she’s been fascinated by black holes. She studied astronomy, physics, and mathematics (“I just couldn’t pick one,” she says during the video call) in Amsterdam, earned her PhD at Harvard, and conducted research in New York. Since last summer – a year after completing her doctorate – she has been teaching at UCSD. The heart of her research: by studying colliding black holes, Broekgaarden aims to understand how galaxies form, and the role massive stars play in that process.
What exactly are massive stars?
“These are stars with at least ten times the mass of our sun. They’re rare – only about one in every thousand stars is that massive – and they live short lives: at most ten million years, a thousand times shorter than the sun. Yet their impact is huge. Their intense radiation and explosive deaths as supernovae trigger new star formation. And during those explosions, heavy elements are created that end up in stars and planets.”
Do we owe anything to these stars?
“Absolutely. The oxygen we breathe and the carbon in our bodies were formed in massive stars. Seventy percent of our body mass comes from them. Astronomer Carl Sagan said, ‘We are made of star stuff,’ but really, we’re made of massive star stuff.”
You aim to study the role of massive stars in the early universe. But how do you study stars that no longer exist?
“Through what they have left behind: black holes. When a massive star goes supernova, its core collapses into something so dense that nothing — not even light — can escape. When two black holes collide, they create gravitational waves — ripples in space-time — which we can detect here on Earth.
“These collisions happen because massive stars are often born in pairs. In some cases, both stars end their lives as black holes that continue orbiting each other. These are the longest engagements in the universe – it can take billions of years before the black holes finally merge. The collisions we observe today are the product of stars that lived in the early universe.”
But if the stars have collapsed into black holes, how can you still learn something about them? Doesn’t all information disappear inside a black hole?
“That’s true, but gravitational waves leave traces. I call my research the ‘paleontology of gravitational waves’: just like fossils tell us about dinosaurs, gravitational waves reveal things about long-lost stars. We build models of how these systems form and evolve, and then compare them to observations made with the LIGO and Virgo observatories – and, in the future, with the Einstein Telescope. Since both black holes and their collisions are rare, we need to run lots of simulations to draw meaningful conclusions.”
What originally drew you to the U.S.?
“One thing was the room for long, high-risk projects – the kind I’m working on. In the U.S., PhD programs take longer than in Europe, which allows for more freedom in exploring different directions. Also, more funding sources are available, including grants meant for bold proposals that were rejected before. That reflects the culture here: growth is encouraged, even if you don’t fit into the perfect mold straight away.”
Did this apply to you as well?
“As a university student, I struggled with impostor syndrome – the feeling that I didn’t really belong. I thought you had to be a kind of Einstein from day one. As a woman, I often ended up in the ‘organizing’ role in group work, which made me insecure – it felt like my content-related contributions didn’t matter. I sometimes didn’t even dare to take a practice test. The turning point came when I got involved in research, which is a fixed part of the curriculum in the Netherlands. My mentors recognized my doubts and explained that this was completely normal. That gave me more confidence, my grades improved, and I completed my master’s with strong results. Today I pass on that experience by showing students that they are good enough, and helping them find the same kind of support that I needed back then.”
Do you still struggle with impostor syndrome?
“Yes, definitely, haha, but I deal with it better now. It came up again in San Diego – I set the bar high, and a rejection, for example for a grant application, can quickly feel like failure. But I’ve learned that there’s no manual for this work, so those kinds of thoughts are pointless.”
You are highly committed to diversity and inclusion – your PhD advisor described you as “a dedicated citizen of astronomy.” How do you handle your own unconscious biases when selecting new people?
“I actively try to reduce them. For example, I never look at grade lists – they don’t say much about potential. Students from less privileged backgrounds or those with imposter syndrome often perform worse, not because of a lack of talent, but because of a lack of support or role models. In conversations, I prefer to focus on motivation and ideas. When you believe in someone, you often see them flourish.”
Your enthusiasm is contagious. But the federal government offers less trust: academic freedom and inclusion programs are under pressure. How do you balance these two worlds?
“It feels incredibly conflicting. Yesterday, I was thrilled by a fantastic result from a PhD student; this morning, I heard that the government plans to cut research funding. Students – in particular international students – feel this uncertainty. I want to offer them all the opportunities, but I can’t always say that with full conviction now.”
Does your American Dream feel shattered with Trump’s arrival?
Broekgaarden lets out a sigh. “It’s tough. I miss my family, my sister is getting married and having a baby. But if I go back to the Netherlands now, I risk not being allowed to return to the U.S. I’d be putting my career and relationship here at risk. That’s really eating at me.”
