Visualizing the Early Universe: My Cosmic Aha Moment

Coming to AAS is, for me, a week-long astronomy seminar. I suspect it is the same way for many attendees, not the least of which because we get to see and hear about results that are very interesting. Now, they may not always be our areas of expertise, but taken together, give us a larger view of the cosmos and its processes.

I always come away with an “aha” moment or two at each meeting. I’ve got several candidates for such moments that will probably translate into a writing project in the next few months, especially in the planetarium and vodcast realms. Let me share one of them with you here.

About twenty years ago, when I first went back to school to study astronomy, I was talking with my advisor (and future co-author) Jack Brandt about the big unanswered questions in astronomy and astrophysics. Of the many we discussed, one resonated with me: how did the first galaxies form? At the time there was not a lot known (or modeled) about dark matter and how it might constrain the early universe; indeed we were less than a year away from the launch of the Cosmic Background Explorer (COBE), which provided us the first good look at the cosmic microwave background.

There wasn’t a good answer at that time about how we got from the first stars to the first galaxies. I remember Jack saying that maybe in 10 or 15 years we’d have better answers, especially after COBE, and maybe later instruments on HST would give us a look at the early universe.

And so, I waited. And every once in a while I asked that question again. And, the answers I got were getting more detailed about the early universe. But, there wasn’t the answer I was looking for.

Well.

Today, 20 years later, I finally got an answer to my question. And, while we (meaning astrophysicists) still don’t have the complete picture (all I’s dotted and T’s crossed), the basic picture is that some 300 million years after the Big Bang, the first stars formed, and they were massive. They were all hydrogen and grew to huge masses. And, high-mass stars live fast lives—dashing themselves to cosmic pieces as supernovae. And those supernovae seeded the cosmos with the elements for second-generation stars (the ones that have more than just hydrogen, but heavier elements and metals). Gravitational condensation and violent activity soon acted to constrain the early universe, going through whole collections of these first stars (called Population III stars). Eventually the first galaxies formed out of this violent chain of activity.

Now, parts of this theory are not new today, but what IS new and what gave me the “aha” I was waiting for, was this: visualizing the early universe with the first stars doing their thing is not an easy thing unless you have a ton of computing power. But, with a supercomputer, you can make a good start. And that’s just what Dr. Volker Bromm and colleagues at the University of Texas-Austin have done. Today, they showed us the work they’ve been doing to probe the earliest epochs of star and galaxy formation. They used the Lonestar supercomputer to create visualizations of the action at the birth of the galaxies.nd, it was while watching those animations that I finally got my “aha”—a visceral understanding of what it might well have looked like ‘way back then. The animations are here and comprise a short peek at what was, at the time I first asked my question, a time in the universe that was really not well explained at all. Today’s explanation takes us a long ways toward understanding that epoch. How long before we can completely and accurately describe it? Soon, I hope. And these simulations are going to pave the way.

The image below is a still from that time, when large stars were blowing their mass into space, affecting the early universe, and setting it to the road of galaxy formation (the rise of structure in the universe). It is amazing to me, and very satisfying, to finally get an answer I can “grok” about something that has fascinated me for 20 years.

Hydrogen density interaction with high-energy, ionizing photons during the formation and decay of eight stars. Visualization by Paul Navratil, TACC.