Astronomer uses computer models to study dark matter in distant galaxies

Photo of the Andromeda Galaxy

“It’s no secret that scientists have got an issue because we don’t know what dark matter is, which is kind of a gaping hole,” explains astronomer Stephanie Campbell.

Stephanie is a PhD student at the University of St. Andrews in Scotland. For their doctoral research, they build computer models that can measure the amount of dark matter in far-off galaxies. To make these calculations, Stephanie has been collaborating with other astronomers to gather detailed data on over 10,000 different galaxies from high-tech telescopes around the world.

Outside their day-to-day research, Stephanie is an avid rock climber, and also enjoys sharing their excitement for all things astronomical through their online and in-person outreach activities.

We sat down to talk with Stephanie about their astronomy research, their science outreach, and more. This interview has been condensed and edited for clarity.

What got you interested in physics and astronomy?

I remember in high school, I enjoyed learning about stuff, and learning how things worked. And I think at one point, I realized I was good at physics. And I realized that doing physics would be a good way to learn the most about as much as I could, if that makes sense. It gives a baseline to learn about the other things.

I know everyone wants the story to be about how passionate I am about space. But I was doing a normal physics degree, which is the exact same as an astrophysics degree at Edinburgh until third year, where if you do normal physics, you have to do weekly practical labs. And I realized I hate labs.

So I decided I was going to do astronomy, which is not the inspirational origin story that people want. But that’s how it happened. And when I started doing astronomy, I realized I enjoyed it way more than normal physics.

Photo of Stephanie Campbell
Astronomer Stephanie Campbell studies the structure and composition of galaxies for their PhD research (Photo Credit: Andrew Perry).

Why is it important to learn about dark matter?

Dark matter makes up 84% of the matter in the universe. So everything that we see and know and love, you know: protons, electrons, the normal stuff that we know about, that’s only 16%, which is not great. And the rest of it is all stuff that we don’t understand in any way at all, which is all in all, not very good.

How do you study the effects of dark matter if it is so poorly understood?

By looking at the effect that dark matter has on the things that we do understand, and we can observe, to see if that can tell us more about how it works.

People (who are not me) run big simulations with dark matter, normal matter, and the whole universe and sort of predict what galaxies would look like if dark matter behaved like this, or what it would look like if it behaved like that. They do their thing, and it’s very computationally expensive and complicated. But what they have in the end is a simulation of a universe.

And then they want to find out what these galaxies really look like, which is where I come in. I can go measure the actual distribution of dark matter and compare it to the simulations and that can help us realize our preferred models.

It’s interesting how much astronomy is very much a big teamwork exercise, because you’ve got people coming at it from all different angles. And it’s really important to be able to interface those different angles together.

Two photos of Stephanie climbing an indoor rock wall.
In addition to their astronomy research, Stephanie also enjoys rock climbing (Courtesy of Stephanie Campbell).

Tell me a bit about your science outreach work.

I am now in charge of St. Andrews’ mobile planetarium. It’s now virtual, but in the future, we will run the mobile planetarium again, which is like a big inflatable dome with a fan. We get all the kids or adults to crawl into this enclosed space and we turn down the lights, so it’s completely dark. We’ve got a custom-made light projector that projects what the night sky will look like that evening. And we can zoom it fast forward and backwards and show them what’s going to be in the sky that night.

This works very well virtually as well, which is good. But it doesn’t have the excitement of a big dark tent that kids love. I think over lockdown we kind of just ground to a halt on outreach activities for so many reasons. School outreach couldn’t happen because teachers were struggling just to do what they needed to do.

Over the last couple of months, the department met and sort of said, what’s our outreach plan? What are we going to do, what activities are going on? And I think it kind of reminded me why I really enjoy managing to communicate what I do.

What do you enjoy about science outreach?

Seeing the self-fulfillment on other people’s faces when they realize that they’ve managed to understand something that they felt they couldn’t understand.

Dark matter is a big popular science buzzword. And I think being able to communicate how we measure it, how scientists know it’s there, and seeing the accomplishment that people can get from realizing that they can understand that too, is what I enjoy the most.

Published by Sam Zlotnik

Sam Zlotnik is a science writer, ecologist, and evolutionary biologist with a B.S. and M.S. in biology and a B.A. in psychology. He is currently completing a Ph.D. at the University of Florida where he studies the behavioral ecology of leaf-footed bugs. Sam writes about a range of scientific topics, from environmental and health news to animal behavior, evolution, and biodiversity conservation. You can read more of their writing at

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