Dr. Colleen Wilson-Hodge is an astrophysicist at the NASA Marshall Space Flight Center in Huntsville, Alabama. She is the principal investigator of the Fermi Gamma Ray Burst Monitor, an instrument that detects gamma ray bursts, which are powerful explosions in the universe.
STEM to the Sky
Jan 4, 2022
The Fermi Gamma Ray Burst Monitor is an experiment that’s looking for gamma ray bursts, which are big explosions out in the universe. This instrument is watching the sky, and it’s my job to make sure that our science data are flowing and to make decisions that involve science. We’ve been in flight since 2008, so this is an extended mission.
I’m also involved in several new missions that are in development. At NASA or other institutions, you write a proposal proposing what you want to do, and that proposal gets reviewed. Currently, I’m working on one mission called the Large Area Ray Burst Polarimeter (LEAP) to go on the International Space Station (ISS). We got through the first step of the proposals, and we’re currently working on the second round. If we get through this round successfully, we get to fly, so it’s a very exciting step to be in.
There are a couple of other missions that I’m involved in that we’re at the beginning of proposing. The reason I’m involved in so many is that not all of them get picked. It’s very competitive, so we have to keep trying until we get one.
Gamma ray bursts are the biggest explosions in the universe. They can come from two neutron stars merging. Neutron stars form at the end of a star’s evolution. They are the densest matter in the universe. When they merge, they produce something called a short gamma ray burst.
In 2017, we saw something very exciting with one of these events. Not only did we see gamma rays, but at about the same time, we also saw gravitational waves, which are ripples in the spacetime of the universe. Those were seen by ground-based observatories called the Laser Interferometer Gravitational Wave Observatory (LIGO). The idea that two neutron stars merging produces gravitational waves was predicted by Einstein. This tells us things about the speed of light and the speed of gravity– that they’re the same within one part in one quadrillion. That event also ruled out some other theories of gravity.
We learned about the densest matter in the universe, and we learned about jets, which are emissions of materials shooting out from when stars merge. Gamma ray bursts are also produced by large stars exploding and forming a black hole. All of this is telling us about the birth stages of a black hole.
The other missions that I’m working on are looking at other aspects of this. Some of them are looking for additional events like the one we saw in 2017 because getting everything together so that we can see it both in gamma rays and gravitational waves is hard. We don’t know where these events are going to come from in the sky.
The LEAP (Large Area Burst Polarimeter) mission is looking at something else called polarization. You might have worn polarized sunglasses before. If you put polarized sunglasses on and look at the water, you can see the fish in the water. If you take them off, you can’t see through the water because of the reflection. This is kind of the same thing.
We learn things about gamma ray bursts, magnetic fields, and the exact details of what’s happening. This is all not a save the world sort of science, but it’s all very interesting. We can only study this kind of extreme physics by looking at things out in the universe. It’s not something we can recreate in a lab.
Neutron star merger event in 2017 (Credit: NASA’s Goddard Space Flight Center/CI Lab)
At one point, I wanted to be a professional hockey player. I never learned to ice skate, so it’s a good thing I didn’t do that.
I got interested in astronomy in about the third grade when the Voyager satellites were first getting out to Jupiter and Saturn and taking pictures. I knew I wanted to study planets back then. In college, I wanted to do radio astronomy. I got a job actually working in the group that I work in now doing gamma ray type work as an undergraduate student. It’s a program through NASA called the Pathways or Co-op Program. That led me to do what I’m doing now.
I got undergraduate degrees in both physics and math. For my graduate degrees, I got a Master’s and Ph.D. in physics at the University of Alabama in Huntsville, Alabama while I was working for NASA. I was doing my Ph.D. work on the same work that I was doing at the time for NASA, so it was very closely tied.
For my work as an undergraduate, there are things I wished I would have known. Some universities offer more hands-on opportunities where you could be involved in things like balloon flight instruments or sounding rocket instruments. These are instruments that only get a little bit of data: the balloon flights last a day, and sounding rockets get five minutes of data. But then you can actually get hands-on experience, which I didn’t really get until later in my career. If you can find those sorts of opportunities and you’re interested in the hardware-type side of things, that’s a really great thing.
Dr. Wilson-Hodge pointing to the GBM detectors on a model Fermi satellite (Credit: Renata Di Gregorio)
There were a lot of surprises. When I first started, I was working on a different instrument called the Burst and Transient Source Experiment (BATSE). It launched about a year before I graduated undergrad, but I was working on it as a co-op student.
The thing that surprised me was that I thought the leaders of the group knew everything at that point in my life. But there were things in the data that they were surprised by. With the way the detectors on an instrument were oriented, they could figure out which direction gamma ray bursts to come from. Some of the first events that the instrument saw came from the Earth, and they were like, Did we get it backward? Did we get a sign wrong? Just hearing these experts say things like that surprised me.
It turned out what happened was they had discovered something– something called terrestrial gamma flashes, which are gamma rays coming from lightning. There are a lot of surprises in the universe, and the experts didn’t know everything. They had things to learn too.
In my early career, the BATSE instrument project I was working on was looking at something called accreting pulsars. These are neutron stars orbiting a regular star. The material from the regular star falls down due to gravity onto the neutron star, and because gravity is strong on the neutron star, it heats up and emits X rays. Those neutron stars have really strong magnetic fields, and that makes any emission that comes out from the poles. So as it swings by, you see a flash of light at the rotation period of the star. There were a couple of pulsars that I discovered in the BATSE data. Every day, we went through the data and looked for new signals. Most of the time, there was nothing new. But there was something new a couple of times, and I was the only person that could see that for just a little while. I was the only person that knew about it, so that was really exciting.
In 2013, I got to work on a project called HEROES (High Energy Replicated Optics to Explore the Sun). This was a balloon flight, hard X-ray telescope. We were going to look at the Crab Nebula and the sun with this telescope on our one-day flight, and I got to do everything hands-on. I tested the detectors, made sure they were working so that we could command while it was in flight. I made sure the voltages were right and looked at the data coming in. We did all of the calibrations, shining X-ray sources on the telescope and getting it all aligned right. This was all very hands-on and a very different experience than other things I’ve done in my career. It was a lot of fun!
HEROES payload on the flight line. The balloon is fully inflated, and the payload is ready to be launched. (Credit: NASA Marshall Space Flight Center)
The event we saw in 2017 opened more questions than it answered because it was the closest gamma ray burst that we’ve seen, but it was also the faintest. It was a lot fainter than you would expect it to be given how close it was. We think it’s because usually for gamma ray bursts, you’re looking straight down the jet that’s coming out. For this one, we were off to the edge. If you think of it like a flashlight beam– how it’s bright in the middle and fades towards the edges– we were thinking we’re looking towards the edge. But there are several different models that could explain that. We’re not completely sure, so we need more events to really understand that.
It also took about a second and a half between when the gravitational waves arrived and when the gamma rays were seen. So, we wonder what exactly is causing that delay. Is it the gamma rays punching out? Is it the black hole collapse time? There are lots of things we don’t know.
Back in 2014, when LIGO saw the first merger of two black holes producing gravitational waves, we saw this tiny blip in the GBM data in the gamma rays. We could really only identify which half of the sky it was in, so we don’t know if it was related or not. Most of the models we have don’t predict any matter that would produce gamma rays or other electromagnetic waves. That would be really cool if there’s more of them.
There’s also the possibility of a black hole and a neutron star merging. Would those produce gamma rays? LIGO has seen a couple of those events, but we didn’t see any gamma rays, and we don’t know if they were pointed towards us or not. There are a lot of new things to explore with those kinds of events.
My days are full of meetings because I work on a lot of projects. Hopefully, I get to carve out a little bit of time to look at data and analyze it.
Before COVID, my job involved quite a bit of travel. I would go to conferences. I would go up to the NASA center at Goddard Space Flight Center in Maryland and to other places pretty frequently to visit and work with collaborators. I miss that part a lot. I traveled probably once a month.
Work-life balance is important to me. I do my best to balance things as much as I can. Now, working from home, people expect me to be available more. I try to carve out time for my family by trying to take the weekends off except occasionally when there’s a big deadline or something.
My home office is upstairs in my house, and most of the living area is downstairs. I’ve made this physical separation so that when I’m not working, I don’t go to my computer.
As the PI of the Fermi Gamma Ray Burst Monitor, I try to exemplify that people should take vacations. I encourage it. It’s hard to do sometimes during crunch time, but when it’s not a crunch, I try to make sure everybody gets a chance to take breaks.
Soft skills are extremely important. In any job, people are probably the hardest part. I’ve spent a lot of time taking leadership classes and classes on how to have difficult conversations with people. A lot of people undervalue the soft skills in technical fields, but when you’re working with a team of people, they are crucial.
In terms of technical skills, having a scientific background is important. It’s also important to know how to program in whatever the language of the time is (currently Python). Math is something I use regularly, calculating various things. I even use trigonometry to look at how long a satellite could contact a ground station.
Dr. Wilson-Hodge with HEROES detectors (Credit: Colleen Wilson-Hodge)
Explore colleges, talk to people, and find out what colleges offer things along the lines you think you’re interested in. But also be willing to change the specialty. As I said, I was interested in planetary astronomy, and then radio astronomy, and then I ended up in gamma rays. There’s a lot of variety.
Don’t be afraid to ask questions. Often, when students have asked me questions, I realize I didn’t explain something well enough. It’s not their fault; it’s mine. I left out something that they didn’t know, or I assume they knew something they didn’t. Sometimes, a student asking me a question makes me realize something important I hadn’t thought of. So, don’t be afraid to ask questions and don’t think everybody knows more than you because they might not.
My kids have enjoyed the various NOVA programs. If you’re interested in gravitational waves, the LIGO website has a huge number of resources available. The NASA sites do as well. Most of the sites have information for students available, so you can learn about different missions and the different sciences that they do.