Galaxy Quenching

0:28Wait, you're listening. can die. Okay, so a galaxy can die or quench in a variety of different ways. Wait, and I'm already going to stop you because that word quench. Yeah. Does that mean like galaxy dimming, galaxy dying? Yeah, we call it death in kind of a way or a dimming of sorts. Yeah. Got it. So I would define it as any process that prevents star formation from happening. Okay. And for stars to form, you need cold, dense gas. You can think of cold, dense gas, mostly hydrogen, as the fuel for star formation. Okay. And so ways that the galaxy quenches is when the stars can't get that fuel?

1:14Yeah, exactly. So, like, what makes that fuel not get there? Well, for example, the supermassive black holes that exist in the center of every massive galaxy, Those supermassive black holes can heat up that gas. Or the supermassive black holes can have these jets that'll actually expel the gas outside of the galaxy completely into the intergalactic space. Okay, so then the stars just kind of starve? Yeah, and that's a term that actually is used in galaxy quenching. It's called starvation because some of this cold gas can come into the galaxy from what we call the cosmic web. Okay. And if that process gets shut off for some reason, then we call that starvation.

1:59So it's like it could get pushed out from the inside or it just stops coming in? Yeah, exactly. Huh. There's starvation, strangulation. Yeah, I'm not sure why these words are so violent. I feel like we could have come up with better ones. The current scientific thinking is that there are at least eight ways that a galaxy can die. That's the theory. But Charity Woodrum has spent her career actually looking. Trying to observe the physical processes that make them dim and sputter out. I'm Lulu Miller and today on Radiolab we have a story of something almost mythic that Charity observed in the darkness.

2:44something I didn't know could happen in space something Charity never expected to see something that would nudge science forward in its understanding of how galaxies evolve and something that would end up nudging her forward ever so slightly through an unthinkable loss

3:07how did you get interested in this like morbid branch of astrophysics? Should I start with all the way back to how I got involved in astronomy in general? Yeah, take us all the way back. How the heck did you end up studying how galaxies die? So I grew up in rural Oregon in a small town called Canyonville. When you grow up in a rural area like that, you get to see the Milky Way. And so being under the dark night sky certainly affected me, and it was certainly a place of peace for me growing up. Was it contrast to, like, in the house, in the school, anything like that? Yeah, I would definitely say that there was chaos at home.

3:54Both of my parents at one time were addicted to some type of drug. My dad, I think one of the words people would use to describe him would be violent. And I think as a distraction, I would go out and look up at the night sky. Just be in the backyard, just walking into the grass and laying down in the grass, sometimes with a sleeping bag. You know, under the trees and just looking up at the night sky. Yeah.

4:26I was thinking a lot about how big the universe is. and how even though I was in my small town, that the world was a lot bigger, the universe was a lot bigger, and there was just more out there to explore.

4:56At a young age, I asked one of my middle school teachers what I could do to work for NASA someday, and he laughed at me. Like a cruel... It was like a chuckle. I don't think he was trying to be cruel, because at the time it didn't make sense to me. I was the valedictorian of our high school, but, you know, looking back, my graduating class only had 17 people. And he also knew my family history. Neither of my parents graduated high school. And just, you know, we grew up in a very low-income area, and so I think he was seeing all of that. There were no other scientists in that town. A lot of the jobs would either be logging or going to nursing school, but I had never heard about a scientist before.

5:43At the time, I was like, okay, I don't know how to do this then. So then what do you end up going on to study? What's the next chapter? So once I graduated high school, my biggest goal, I guess, was to escape poverty, and I became a registered nurse. But once I started working as a nurse, I couldn't handle the emotional toll of it. Just seeing human suffering on a daily basis, like an older person not getting visited, or even, you know, once a week there would be something absolutely catastrophic that you would see. And I found myself just thinking about it all the time, and it was really affecting my daily life.

6:25So at the time, Jason, what would be my future husband, one of his coping mechanisms was to read books. He read, you know, hundreds of books a year. And yeah, he was like, why don't you pick up some books? Maybe that will get your mind off of it. I started picking up popular science books by, you know, like Carl Sagan and Stephen Hawking and started reading about those. There's a particular image actually itself that's one of the main reasons that I went back to school to study physics. It's called the Hubble Deep Field. Hubble Deep Field. Okay. I encountered it in one of those books. And basically this image, how it was made was they found the darkest part of the sky.

7:06So as far as we knew, there was nothing there. And some astronomers said, why don't we point the Hubble Space Telescope at this dark patch of sky for 10 days? Which was a very kind of bold and crazy move because Hubble Space Telescope time is very precious and expensive. And some people thought nothing would be there. Like, why point it in complete darkness? And yeah, they used Hubble to stare at this dark place in the sky for 10 whole days. And then the image that came back had thousands of galaxies in it. Thousands. Thousands? Yes. You can easily pull this image up. Just Google the Hubble Deep Field.

7:48It looks like someone threw glitter on a black floor. And there's like some bigger pieces that feel closer. And there's all different colors. I see greens and yellows and oranges and blues and whites. And so are each one of those dots a galaxy? If it's very bright and has those spikes around it, it's a star with, you know, a star in between us and those galaxies. But everything else is an entire galaxy. Wow. She said you could also see where the dying ones are. There's some red orb galaxies. Oh, there are? Yeah, yeah. Oh, are they like these orangey ones? Yeah, they're really red. We call them quiescent galaxies when they're red and dead like that.

8:32Oh, quiescent, like quiet or dormant, like it's there, but it's not making new stuff. Right, exactly.

8:42And so I was just sitting there staring at that image. Each of those galaxies has billions of stars, and each of those stars we think has at least one planet. Wow. And I don't know, it kind of gave me the feeling that I got as a kid laying under the night sky. And it also just kind of calmed me. I wasn't thinking about that human suffering that I was seeing on a daily basis.

9:11I was actually nine months pregnant when I walked into an academic counselor at the University of Oregon and said, hey, I'm a registered nurse, but I want to go back to school for physics. Wow. He looked at me like I was crazy a little bit. But around the time when I was pregnant with my son, I was thinking about, you know, what type of person I wanted to be for him. Because I wanted him to pursue his biggest dreams. And I felt the only way to do that was to pursue mine. And how was that going to work? What was Jason doing? He had a soil company business. He would literally sell dirt to people.

9:49He loved soil. And that was his big passion because he loved, you know, reading about all the bacteria and the soil and how it was alive and all of that. And so we always made the joke that whenever he was looking down, I was looking up. So at first, you know, I have a new baby now and I'm starting my first term. And so I wanted it to be a little bit easier and only be gone away from Woody for, you know, an hour or two a day. I didn't want to be away from him for too long. Was Woody short for anything or Woody is his name? name. Yeah, that was his given name. So, okay, Woody's a little baby. Yeah.

10:25And on the first day of class, I met Dr. Scott Fisher, who was an astrophysicist. And he, you know, he wasn't Stephen Hawking or Carl Sagan. He was like a normal person that had this job that I, and that was the first time I realized like, oh, I could actually have a job in this field. You have a job. You got healthcare. You got a salary. Yeah. And you get to think about this stuff. Exactly. I was Like, okay, that's what I want to do now. So after taking that first day of class in Dr. Fisher's class, I started bugging him every day. And I would just go to his office and ask him if I could join his research group.

11:00And he'd be like, you know, my research group is full. Come back later. So I'd be like, okay, come back a week later. A week later? Yeah, it was really annoying. And so he said, you know what? His boss had a research project for a student. And so she asked if he had any students, and he was like, well, there's this one girl that won't give up, so let's go with her. And she worked in the field of galaxy evolution.

11:32The research group was Charity and three other undergrads, and they called themselves the Cosmic Wolf Pack. And together, they taught themselves how to read the flickers in the sky, how the blue ones were newborns and the red ones were dying. She said they'd often get yelled at for squealing too loud when some new image came back showing galaxies of beautiful colors or shapes, clusters. And almost every weekend over the summers, I would go up to Pine Mountain Observatory, giving people tours of the night sky with one of the bigger telescopes up there. and Jason and Woody would camp. And before Woody's bedtime, they would be in the dome with me as I was talking about the night sky.

12:15And then they would go sleep in the tent and wait for me to get done, which would, you know, be much later, much past Woody's bedtime. The first year, I would have to go back to breastfeed him quite often. So I actually would have to shut down the dome and say, I can hear my baby crying in the distance, he's hungry. And so I would go feed him and then come back. In the sleeping bag, just like cozied up? Yeah. So, this must have been when he was around two years old. There had been a lot of cloudy nights all in a row. And we stepped onto the porch one time, and it was a clear night sky. And he looked at me and he said, oh, thank you, Mom.

12:50I said, for what? And he said, for turning the stars on. So, he thought that when I was giving people tours of the night sky that I was the one that turned the stars on at night, I guess. And I looked at Jason, and he was crying. Was it like a battle with Jason? Was Jason like, Woody, look at the soil? And you were like, Woody, look at the stars. And you won. No, I would say it was quite equal because Jason loved vegetable gardening. And so Woody was often in the garden with Jason. And they would come inside to eat lunch and then leave again back to go gardening. And I knew where they sat because there would be four little piles of dirt from where they had sat down.

13:31Yeah. Yeah, he was, they were both very sweet.

13:42At what point do you learn about rejuvenation in this story? So that happened when I was in my second to third year of graduate school. And can I just ask, like, for setting in time, is this before or after the worst day? This is after the worst day. So the worst day happened my junior year in the physics program. okay so I guess for chronology maybe we we do this to the degree that you want to however you want to talk about it do you want to do you want to take a break first you want to just plow through how do you want to go let me take a sip of water real quick and then I will yeah we'll be back in a moment.

14:30I guess just can you say what happened on January 15th, 2017? Yeah. So it was a long weekend and me and my son and husband decided to take a mini vacation to the Oregon coast. and it was especially sunny on the Oregon coast for it being wintertime. And a lot of people that are not from the Pacific Northwest might not know about this, but there's these things called sneaker waves and we were walking along the beach and the water would come up to the same place every single time and I was walking a little bit ahead of them and one of those sneaker waves, you know, hit them and swept them out to sea.

15:20My memory, you know, fades in and out on that day. I eventually found myself in an ambulance, and my eyes were closed, and I felt a banging on my head. And I woke up and realized I was hitting myself in the head saying, you know, wake up. This can't be real. And, you know, then I realized it's getting dark outside, and I had heard that the Coast Guard was going to call off the search once it got dark. And so then I guess I started freaking out because apparently I jumped out of the ambulance door through the back and just started running towards what I thought was the ocean. But I actually didn't see the ocean nearby.

15:58I didn't know where I was. I'm barefoot. One of the cops, you know, pulls me back into the ambulance. And I guess I did that a couple of times. Yeah, eventually they drove me to the hospital. and I guess I was just screaming a lot and, you know, couldn't, I was just screaming. And so a nurse came up to me and had a pill in her hand and she said, do you want to just fall asleep? And I took that pill.

16:32And I was hospitalized like that for about five days, I believe. I woke up and I realized, you know, it made national news that, you know, Jason and Woody had been, you know, swept out to sea. Is there anything in running through the field? Was it like wanting to find them? Was it wanting to join them? I feel like it was, I was trying to, I realized they weren't going to search for them anymore and I wanted to find them. I think that was my intention. They took that as me being suicidal. I didn't think I was, but I've heard people say that they thought that I wanted to join them. So they sent me to a psych ward.

17:22But the next morning, I had a meeting with the psychiatrist there, the psychologist, and I said, I can't be here. There was nothing to do. There were books, but I found that I couldn't even read. I would try to read, and I couldn't even read. Meaning you couldn't make sense of the words, or you just—it felt too flat? Like, it didn't—it felt like I was reading the words, but I wasn't processing them, if that makes sense. I've never tried to describe that before. But, yeah, I couldn't read the books. And I was afraid to watch any TV because if a scene of the ocean would come up, I would have a panic attack.

18:04And so that's what the first week looked like, basically. So after being released from the hospital and the psych ward, there's no way I could have walked back into the house that I shared with Woody and Jason. I went and stayed with close family. and those first few weeks, I didn't leave the couch really. I would just lay there and laying on that couch, I really felt like I could feel the life going out of me because there was nothing left for me, I felt like.

18:47Where do you go? Yeah, so I knew I had to do something and I knew that laying on that couch wasn't going to get me that desire to live back. And I remember people close to me, they apparently had this group chat and they always made sure that one of them was at my house with me at any given time for those first few weeks. And they knew that as a kid I loved school and thought it would be a good distraction for me, I think. And so they said, why don't you go back to school? and actually when I told Dr. Fisher that I wanted to go back to school during that meeting he was crying and he said you know your life is turned completely upside down nothing's the same so if you want to come back to the research group the research group would be exactly the way it was before this can be the one spot that never changed hearing him say that was a huge reason I was able to go back.

19:43But when I went back to school, when people would see me for the first time, their eyes would kind of look like a deer in headlights, like, oh no, what do I say to her? And also I looked very different. I normally wear a lot of bright colors, but I was wearing the same black hoodie and black leggings every day. And I was 15 pounds lighter. And I think I wanted people to see that I was different now. I wasn't the same person I was. But at the same time seeing their reaction, that was hard. So she looked up.

20:22I'm an extra galactic astronomer, so I study galaxies outside of our own. And to do that, to find those distant galaxies, what you have to do is exactly what they did with the Hubble Deep Field. You have to find the darkest part of the sky and look at it. And that's literally what I do, is just look in the darkest places and try to find light there.

20:59She graduates college, starts grad school, and keeps looking. into the dark, day after day. And when she'd see a faraway sprinkle of galaxies, she'd focus in on the red orbs, the dying ones, the dimming ones. And she'd perform autopsies, trying to figure out whether it had been something from the outside or the inside, which caused it to lose its light. Day after day, galaxy after galaxy. And then one day, 1 ,639 days after the worst day, she saw something odd. She was looking at this one group of eight dimming galaxies. They were massive quiescent galaxies. Quiescent, which means they were not making new stars, so they're that kind of like holding pattern red, slowly dying but still emitting light vibe.

22:09And getting the data back, the first scientists that looked at these galaxies found that four of the massive quiescent galaxies had cold gas reservoirs and four of them did not. Huh. Yeah. We do know that cold gas reservoirs are the fuel for star formation. And so was that at first puzzling? Because you're like, the whole thing about why they die is like, it's pushed out or it's heated up or it's ejected. And you're like, but the food is right there. It's there. Yeah, exactly. So why do some of them have the cold gas reservoirs and some of them don't? So she started measuring everything she could think of, sort of taking the vitals of those galaxies with cold gas reservoirs.

22:50She looked at their metal composition, their growth charts, how they had grown in stars and mass over time. One of the things that I was able to measure was what's called the star formation history of the galaxy. So think of that as on the y-axis, there would be the star formation rate. So how many stars these galaxies are forming per year. And on the x-axis, you have time. And so their early star formation histories, when they were younger galaxies, those all looked quite similar. However, in the last billion years, all of the galaxies that had the cold gas reservoirs in the last billion years of the galaxy's life, there was a bump in their star formation.

23:32There was this significant amount of what we called secondary star formation episodes or rejuvenation. Wait, so meaning like these dying, dimming galaxies, the ones that had the gas were making new stars from a place of death. Yeah. What? Yeah, and people had seen rejuvenation before, but I don't know that anyone had seen cold gas reservoirs in massive quiescent galaxies and saw that they also had rejuvenation episodes. Like you saw the physical matter of what it takes to come back to life for a galaxy. Yeah, exactly. Then does it still sputter out? Or could it ever get back into real star formation?

24:23Could it ever keep going and get alive again? Yeah, definitely. Oh, it could. Yeah. Just like with the physical processes that can make a galaxy quench, There's physical processes that can make a galaxy rejuvenate as well.

24:41Broadly speaking, there are four main ways that a galaxy can come back to life. One, it can happen from within. The black hole at its center surges with an unexpected burst of energy that allows new stars to form. The rest of the ways happen from without. A sudden inflow of gas, a huge collision. Two galaxies collide and, you know, eventually form one galaxy together. Or, wildest to me, and what Charity believes caused rejuvenation in the galaxy she was looking at, just a little boop. If two galaxies even interact with each other and do like a flyby, where they just fly by each other, that little interaction can cause bursts of star formation as well.

25:26No. Yeah. And like can bring it back to life? Yeah. Just like a drive-by encounter? Yeah, just like seeing a friend and it, you know, lifts your mood.

25:48My childhood best friends, they're the biggest reasons I was able to survive and make it to where I am today. When I was laying on that couch, the people coming over and helping me had no reason to other than that they loved me. And I don't think a lot of people get to know who those people would be in your life, and I know who they are. There was her brother. He sat me down and told me, you know, me and his wife Gina and the artist Claire wrote a song for you and we want to play it for you. They weren't afraid to talk to me about what happened. They just wanted to be there. There was the cosmic wolf pack.