On Astrophysics, Stardust, and Our (Teeny Tiny) Place in the Universe 

Katie Mack brings galactic ideas down to earth

By Katie Mack, as told to Steven Boyd Saum

Katie Mack (BS ’03), a theoretical astrophysicist at North Carolina State, studies some of the most complex topics in the cosmos—dark matter, galaxy formation, and the origins of the universe. But she is best known for her ability to bring those ideas back down to earth. Her ability to communicate complex science to the general public has made her an in-demand interview for radio, television, and podcasts, and she has written for Scientific American, Slate, Time.com, Sky & Telescope, and Australia’s Cosmos Magazine. Here, Mack talks about the importance of keeping the stars within reach.

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Here is a thread I posted on Twitter one Friday night: 

I feel the need to tell you a thing about being stardust.

Yes, you are made of stars. Yes, you, in particular.


All that carbon, oxygen, nitrogen, etc.—that was all made in stars. Most of your body is made of that stuff: atoms that a star forged inside itself or at the moment of its unimaginably violent death.

So, yes, you are stardust. But only if you count by mass. If you count the number of atoms in you, most of those?


Never part of a star at all.

Most of your atoms have been in the universe for 13.8 billion years.

Most of your atoms were forged in the Big Bang itself.

I think it’s cool that we are made of stars, that our planet and our bodies and everything we touch can only exist because of the nuclear alchemy in the hearts of stellar infernos.

But I think it’s MUCH cooler that most of our atoms have been in the cosmos all along.

You are stardust. And you are the ashes of the Big Bang. And you are, at every imaginable level, a creation of the Universe, vast and beautiful and suffused with unbridled power.

When I was growing up, my mom was really into science fiction. I used to borrow her books and magazines. I was always excited about things like Star Trek, and I read A Brief History of Time and did a lot of reading about physics and astronomy. I was fascinated by big-picture questions: How does the universe begin? What are black holes? What is space-time?

I remember when I first started to think of the world as a planet—that we are a rock in space. It is not always something that you think about in your daily life. If you do, you get a feel for where you fit into the larger universe and the fragility of human life. The atmosphere is only about 100 miles thick. That’s not much.


I like being able to help people see the universe in a different way—or understand physics concepts that they haven’t thought about. You have a special kind of power when you understand something that was always opaque before. I like to help people find that power for themselves.

Take dark matter, for example. We don’t know exactly what dark matter is made of. But, observationally, it’s surprisingly simple: It’s just matter—stuff that has mass—that happens to be invisible. When you talk about it like that, it doesn’t sound as exotic. But then there’s a lot of detail you can get into: how it’s distributed in the universe, how we know it’s there, how we’re trying to figure out what it’s made of. There are so many pieces of evidence for it, but we still don’t know what it is. So the quest to figure it out is like solving a mystery. 

Or take black holes. Why is it important that we understand black holes? For one, they’re ubiquitous in the universe. There’s a massive black hole in the center of every large galaxy. They’re extreme objects, with properties that nothing else has. They change the behavior of space and time. So, more than just the end state of a star, foundational questions of physics are tied up in the way that black holes interact with space and time and information. 

You are stardust. And you are the ashes of the Big Bang. And you are, at every imaginable level, a creation of the Universe, vast and beautiful and suffused with unbridled power.

We use black holes to study gravity, to study how matter builds up in the universe. Hopefully, soon we’ll be able to use other kinds of gravitational wave detectors to study how galaxies form, because we’ll be able to catch larger black holes colliding. Even now, we’re testing the parts of general relativity associated with gravity by watching the collision of black holes—sometimes a billion light years away.

It’s mind-boggling just how much there is out there that we still need to know—everything that’s being discovered, new ideas in science. There’s so much I want to explore and study and calculate. I’m in the wonderful position that I get to pursue my curiosity. There’s just too much interesting stuff in the world; that’s my biggest problem.

Follow Katie on Twitter @AstroKatie