...why our galaxy is a spiral? (bonus episode with Devin Waller)

Perry Roth-Johnson: 0:05

Hello! This is Ever Wonder? from the California Science Center. I'm Perry Roth-Johnson. Today, we have another bonus episode for you before we go on break for the holidays. This is an extra special one, because I'm going to introduce you to Devin Waller, who will be my new co-host for the next few episodes. As we wrap up our first season, we're going to answer a question from one of our listeners and give you a teaser of what's coming next season. Devin Waller, you are the air and space exhibit project manager at the California Science Center, and now you're also the co- host of the Ever Wonder? podcast. Hi Devin!

Devin Waller: 0:44

Hi Perry. Thanks for having me on.

Perry Roth-Johnson: 0:47

Hey, thanks for joining me. Um, so you and I work together almost every day at the Science Center, so we know each other quite well. But for our listeners who might not know you yet, uh, why don't you introduce yourself?

Devin Waller: 0:57

So, hi, everybody, as Perry just said, we've worked very closely at the Science Center. Um, I'm the air and space exhibit project manager, and I work closely with the curators, like Perry to manage the fabrication and the installation of all the air and space exhibits that we have on-site.

Perry Roth-Johnson: 1:14

Perfect. So in addition to managing those projects, uh, you're also a scientist by training, which is just the kind of person I need. Uh, because we actually got an email from one of our listeners--or really from Emmanuel's parents who wrote,"My child was wondering: why did the dust in our galaxy form in a spiral way?" So Devin, can you help me answer Emmanuel's question?

Devin Waller: 1:35

I can. So I have a background in science. I have degrees in astrophysics and planetary geology. So let's see if we can, let's see if we can get through this question. Um, it's a really great question. Galaxies--they come in many different shapes and sizes, actually. Most of them are spiral probably about three-fourths of them. Um, so let's start by talking about what a galaxy is. So a galaxy is you could think of that is just a densely clustered grouping of stars. Um, some of them are so big, like, like our Milky Way, that they can have these super massive black holes at their centers. So spiral galaxies, typically you have this big central grouping of stars, and then you'd have these huge spiral arms that come out from the center. Each of those arms, uh, can carry, you know, tens to hundreds of millions of stars within them. So a really big cluster. When looked at from the side, you can see that a lot of galaxies are, are very flat. They're like these, these thin almost like pancakes on the side, they're very thin, but they have this big central bulge of stars. The reason why galaxies are spiral in shape has to do with how they're formed. Scientists think that the galaxy is formed from a gigantic molecular cloud. And this cloud, it's not like the clouds that we have here on Earth--but it's made up of gas and cosmic dust. And so what happens is you have this big thing of gas and dust, and then somewhere nearby, there could be this gigantic disturbance. It's an explosion of some sort. It could be from an exploding star or a supernova explosion. And that that explosion will cause a shock wave that interacts with this cloud. And when that happens, the cloud will start to condense onto itself. It'll start to just pack compact down onto itself. And as all of this material is getting denser and denser, the cloud is--and it's still amorphous, it doesn't really have a shape--but it starts to spin, faster and faster and faster.

Perry Roth-Johnson: 3:46

Why does it start spinning?

Devin Waller: 3:48

Yeah. So why does it spin? And so here's an analogy. So think of like an ice skater who is out on the ice, um, doing a spin. If that ice skater puts their arms out to the side, they'll spin at a certain speed. But as that ice skater brings their arms closer into their body and say they wrap them around their chest, they'll spin faster and faster. And it's because of the conservation laws of physics it's angular momentum.

Perry Roth-Johnson: 4:18

Okay. So you're saying just like a ice skater would spin faster as they bring their arms closer to their, their chest, their body, this cloud of gas and dust--when it gets pushed closer together by this shock wave, uh, from a dying star that exploded--it's also kind of pushing itself closer to its middle. And so that makes it spin faster and faster. Um, but how do we get to the spiral shape?

Devin Waller: 4:42

So as it starts to compact in and of itself, it will flatten out on its edges. And just because of the sheer speed at which this thing is moving and as the edges of the galaxy start to flatten out, um, the stars that are clumping together, um, will form these arms will, will form the arms of the galaxy. And that's just because of the force of gravity and that's how you get the spiral shape.

Perry Roth-Johnson: 5:10

Awesome, thanks! Well, Emmanuel, I hope that answers your question. And to our other listeners, if you have a question you've been wondering about, send us an email to everwonder@californiasciencecenter.org to tell us. So Devin, I'm glad you could help me answer that astrophysics question. But, uh, whenever I hear you get introduced, it's a little differently, uh, especially like when our colleague Ken Phillips--who co-hosted with me on an earlier episode--Ken will introduce you often as a planetary geologist by training. So, which is it, are you an astrophysicist or are you a planetary geologist?

Devin Waller: 5:41

Um, so I have, I have both of those degrees, but it is kind of funny because I often tell people that I accidentally majored in astrophysics and it's actually partially true.

Perry Roth-Johnson: 5:53

Wait, really? How do you accidentally major in something?

Devin Waller: 5:55

I know. Um, so when, when I was in high school and you know how you have to choose, um, a college major by the time you're, you know, in junior year, you start to think about what you're going to do for the rest of your life. And so there was a couple of major events that happened when I was in, you know, in the junior year of high school. One, NASA had this historic achievement. So after about two decades of not going to Mars, they landed a rover on the Martian surface. And it was on every major newspaper and magazine you could think of. It was sort of all over the magazines that you see at the supermarket checkout line.

Perry Roth-Johnson: 6:43

Okay.

Devin Waller: 6:43

And so this was super exciting! So remember I was trying to figure out what my major would be. And I had always had an interest in planetary science and, and the planets in general. I was the type of person that would watch all of those science documentaries. And so when this happened, it just, it interested me so much. I thought it was the coolest thing. And about the same time--so coincidentally, within that same month, there was a movie that came out and it was called"Contact," and...

Perry Roth-Johnson: 7:15

Oh, I remember"Contact"!

Devin Waller: 7:16

...yes, and"Contact," it starred a younger, Jodie Foster and she played an astrophysicist, right. And spoiler alert: she like discovered this signal from an alien civilization. But what made that would be so interesting with me, to me, were two things. One, it's a woman and she's playing an astrophysicist and I, it, she sort of encompassed everything at that point that I just, I wanted to be. I wanted to work on an active mission like that. And so I felt like it just all clicked when I saw the movie and I read those, um, I've read about that historical event that NASA put together. Um, I had a plan. I wanted to be, you know, go in declared with astrophysics and I wanted to study Mars.

Perry Roth-Johnson: 8:06

So you want to be a young Jodie Foster, driving rovers around on Mars.

Devin Waller: 8:10

Exactly.

Perry Roth-Johnson: 8:10

That was like your dream at the time.

Devin Waller: 8:12

Exactly.

Perry Roth-Johnson: 8:13

Okay. So what was the problem with that?

Devin Waller: 8:16

So it was shortly after I actually started, uh, taking classes. I realized that, you know, there aren't, um-- you, when you study astrophysics, you don't study those small rocky planets, and it wasn't exactly what I thought it was going to be. Astrophysics is an amazing, um, study. You know, you're studying the physics of the cosmos, the, the physics of the universe. And you're asking a lot of the big questions, kind of like the one that Emmanuel asked, um, in his email. About, you know, what is the structure of a galaxy? And how does a black hole form? Or what is dark energy and dark matter? But it's not asking those questions, like what is the chemistry and the mineralogy of the rocks that are on Mars? You know? So you're, you're not asking the questions about what the composition of those little rocky planets are.

Perry Roth-Johnson: 9:19

Okay. So you wouldn't like send a rover to go drive around a galaxy arm and figure out what it's made of.

Devin Waller: 9:26

Exactly.

Perry Roth-Johnson: 9:26

You would send a rover to Mars. So when did, when did you realize all this? Like, you can come in your, your guns blazing, you're doing astrophysics. You want to study Mars. When do you figure out that there's a mismatch here?

Devin Waller: 9:38

Yeah. You know, I really didn't put it all together until almost the end of my second year in college. But by that time I was fully devoted to getting this degree in astrophysics--and besides, I mean, it's super cool stuff, you know, you're learning! Black holes and galaxies and stuff. So I figured it was a great foundation. I would finish the degree, and then, hey, if I wanted to study planets, I do it. You know? I get another degree. I come back to college or I'd go to grad school after that.

Perry Roth-Johnson: 10:06

Okay. Hilarious. So whether it's astrophysics or planetary geology, you obviously have a lot of expertise when it comes to space. Um, but you didn't just come on today to answer our listener question. You are coming back on the podcast. I know you're working on some amazing new episodes about space exploration for next season. Uh, we've been reaching out to people, uh, interviewing some of your grad school friends, uh, when you were studying Mars and the Moon, and asking them to be guests on our show. Can you give our listeners a little bit of sense of what to expect in the new season?

Devin Waller: 10:38

Yeah, I'm really excited about what we have coming up. Um, we have some really great people that are coming on to the show. We have, um, one person that's coming on--she works, um, she works for NASA JPL, the Jet Propulsion Laboratory--and she's an actual Mars rover driver!

Perry Roth-Johnson: 10:56

What??

Devin Waller: 10:56

So she'll be able to answer those questions.

Perry Roth-Johnson: 10:59

Alright, who else we got?

Devin Waller: 10:59

We have another person that's coming on. Um, she is a geologist who looks at different, uh, field sites here on Earth. And she, um, she compares them to the chemistry and the geology that you see on the Moon and Mars. And she trains astronauts so that when they go to, to the Moon and eventually Mars, they'll be able to do the same kinds of geological tests and studies there as they do here.

Perry Roth-Johnson: 11:33

How cool. So she, like, one of these people gets to hike around the volcanoes, like places on, on Hawaii where there's all these black rocks and it looks like you're on the Moon. Uh, and they, they, she brings the astronauts there, so they learn how to be geologists when they actually fly to the Moon?

Devin Waller: 11:48

That's exactly right. And I think she has a few stories to share with us too.

Perry Roth-Johnson: 11:52

Well, Devin as lifelong space nerd, I am super pumped and excited for this new season of Ever Wonder?, and I hope our listeners are too. Uh, thanks for joining me today. And I'm looking forward to doing more shows with you.

Devin Waller: 12:03

Yeah, of course. Thank you for having me and I look forward to the next season.

Perry Roth-Johnson: 12:08

That's our show, and thanks for listening! Until next time, keep wondering. Ever Wonder? from the California Science Center is produced by me, Perry Roth-Johnson, along with Jennifer Castillo. Liz Roth-Johnson is our editor. Theme music provided by Michael Nickolas and Pond5. We'll drop new episodes every other Wednesday. If you're a fan of the show, be sure to subscribe and leave us a rating or review, or tell a friend about us. Now, our doors may be closed, but our mission to inspire science learning in everyone continues! We're working hard to provide free educational resources online while maintaining essential operations like on- site animal care and preparing for our reopening to the public. Join our mission by making a gift at californiasciencecenter.org/support.