Dr. Joanna Berteaud (she/they)

Astrophysicist
X-ray Astrophysics Laboratory (662)

What inspired you to pursue a career in astrophysics?

For a very long time, I wasn't sure what career I wanted to pursue. In elementary school, I wanted to be an archaeologist, and later I thought about becoming an interpreter. But I've always really liked science, and, above all, I've always loved learning. After high school, I studied mathematics and physics, and it was so fascinating that I wished I could do that every day of my life. Soon, I realized that a way to achieve this would be to become a researcher. Choosing between mathematics and physics was hard, but I told myself that by doing physics, I would keep doing mathematics, too. Moreover, I was really fascinated by the mysteries of the Universe, and I wanted to contribute to its understanding, so I chose astrophysics. However, the research I am doing today has impacts in other fields of physics.

What science questions do you investigate?

I investigate the nature of exotic matter. “Exotic” matter refers to a type of matter that is poorly understood, either because of the extreme conditions it requires to exist, or because its fundamental nature is unknown. Namely, my research aims to better understand dense matter and dark matter. These topics sounds like they have more to do with nuclear physics and cosmology than astrophysics, but I truly am an astrophysicist; to understand exotic matter, I study neutron stars and their multiwavelength emission. Neutron stars are the collapsed cores of massive stars and therefore one of the end states of stellar evolution. They are fast rotating, highly magnetized and very compact objects that offer unique physics laboratories harboring extreme conditions.

The core of neutron stars reaches several times the nuclear saturation density, that is, several times what our best experiments can achieve on Earth. Through analyzing their X-ray emission, we can measure a neutron star's mass and radius, which helps us put constraints on the properties of dense matter. This is the primary goal of the Neutron Star Interior Composition Explorer (NICER), an X-ray telescope on the International Space Station, whose team I joined when I started at Goddard. I use machine learning techniques to speed up our analyses that currently take weeks to months.

I also use X-rays to identify millisecond pulsar (a sub-type of neutron stars) candidates in the Galactic bulge. More than fifteen years ago, the Fermi Large Area Telescope (LAT), a gamma-ray telescope, detected an excess of photons coming from the Galactic center. Its origin remains unknown to date, but scientists made two hypotheses: either dark matter annihilation, or unresolved millisecond pulsars. Finding a population of millisecond pulsars in the bulge would be a major breakthrough for understanding of the gamma-ray excess and would help us constrain the nature of dark matter.

Who inspires you?

The people that I am in a mentoring relationship with are usually the ones that inspire me the most. I really look up to my past and current advisors, who have taught and continue to teach me how to be a good scientist. I admire their work and achievements, and I hope to become as brilliant as them one day. I also take inspiration from students and interns I work with. Interacting with them teaches me a lot.

What do you enjoy the most about your job?

My job offers a lot of unique and amazing opportunities. First and foremost, I get to work with the people I admire the most. I interact, every day, with people I look up to. I also get to meet people around the world and work in different countries. Those are enriching experiences. The downside is that I often have to say goodbye to colleagues that became my friends when one of us is transitioning to a new position. Friendship is stronger than distance though, and I am proud to say that I have friends around the world.

What science question intrigues you the most?

I am of course very intrigued by the nature of exotic matter in our Universe, but I feel like giving this answer is taking the easy way out. So, let me tell you about another scientific topic that fascinates me: prime numbers! It's a really simple concept, that leads to a large number of complex questions, including many problems that remain open and unsolved to date. I wish someone would demonstrate Reimann's hypothesis, Goldbach's conjecture or that there are infinitely many twin primes while I can witness it.

What is one of your favorite moments in your career so far?

I defended my PhD thesis on July 3rd, 2023, and this was one of the best days of my life. I was so proud to present my work to my peers and get very positive feedback from them. After my defense, I had an extraordinary feeling of achievement, which confirmed that choosing astrophysics had been a right decision. My friends also organized a scavenger hunt for me, each enigma leading from one side of our laboratory to the other, and I had so much fun. Isn't that a beautiful metaphor for the research world?

What is one thing you wish the public understood about your field of work?

I wish everyone understood that astrophysics, and science more generally, is for everyone. It's not for people of a specific gender, or from a certain region of the world, or from a given social background. The only thing you really need is to be naturally curious. If you are interested in science, nothing should stop you from studying it. Today, not everyone has the same access to education and employment, but the world would be a better place if we all had.