ESA/Hubble & NASA and S. Smartt (Queen's University Belfast)
LUMINOUS WORLD: The galaxy NGC 3521, classified by astronomers as a 'flocculent spiral' due to its woolly appearance, resides 40 million light years away in the constellation Leo.
Last month, I interviewed Amber Straughn, an astrophysicist at NASA’s Goddard Space Flight Center who studies the evolution of galaxies. She's part of the team working on what will essentially be the most powerful telescope ever built:the James Webb Space Telescope, which will succeed Hubble as NASA's premier observational laboratory after its launch in 2018.
I spoke to Straughn for our 2016 Visionary Arkansans issue (she's a native of Bee Branch, though she lives in Maryland today), but my short profile for the print edition of the Arkansas Times could only briefly touch on her work. Because I found our conversation to be so illuminating and because Straughn is such an effective communicator, I wanted to publish a more complete transcript of the interview. (I call it an interview, but really I just demanded that she teach me science over the phone for 45 minutes.)
Among other things, Straughn and I discussed the engineering challenges behind the JWST, its potential to advance our knowledge of exoplanets (planets outside the solar system), and her research into the galaxies of the early universe. This transcript has been edited for clarity, and I've annotated a few sections with explanatory notes and links (including some Wikipedia links, which you should take with a grain of salt).
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BENJI HARDY: Tell me about your background. What got you into this work?
AMBER STRAUGHN: Being from Bee Branch. The sky there was and still is beautiful and dark. And that really is what got me into astronomy as a kid — the beautiful, dark, rural sky.
STAR GAZER: Amber Straughn, astrophysicist.
Would your family go stargazing?
I would often drag them out to look at the stars, so it was usually initiated by me, but yeah. I’d figure out when the meteor showers would happen and drag them out to see those, and eclipses.
I went to Southside in Bee Branch and graduated in ’98. I was interested in science as a kid generally, and, of course, I went through a phase of wanting to be an astronaut. I was always interested in either medical research or astronomy ... [But, astronomy] always won out, because I just loved the sky so much.
I’ve got to ask. Was it difficult being a young girl in a small Arkansas town who was really into outer space?
Yeah, of course. Just the typical — what you would expect. I was a nerdy little kid that was interested in science. [laughs] My family, we’re from a rural community and neither one of my parents went to college. [It was a] blue collar community, so it was a little weird that I wanted to leave and study space.
But you know, my family was always super supportive of me, which is awesome. They didn’t have technical jobs, but my mom has always been my biggest cheerleader my whole life, and still is. She's still in Bee Branch. My dad passed away when I was in high school, but he was always supportive of me too, and I feel like he really instilled the value of hard work in me. He always had more than one job: He raised beef cattle, he was a mechanic, he had a dairy farm. He was the epitome of hard work, and it took a lot of hard work for me to get through grad school and to work for part of that time.
I went to the University of Arkansas, and majored in physics there. I graduated in 2002 and then went to Arizona State University and got my masters and Ph.D. in physics at ASU. I’ve been here at NASA Goddard for eight years now — I started here as a postdoc in 2008 right after I got my Ph.D. I was doing astronomy research under the [James Webb Space Telescope] team, and then I was hired on as a civil service astrophysicist in 2011 to keep working on the JWST team.
JAMES WEBB: A crew working on the telescope's hexagonal mirror.
What's your role on NASA’s James Webb mission? Describe what the telescope is and what it will do.
I’m on the project science team. That’s the team of scientists here at NASA that works alongside the engineers, and also, of course, with the broader astronomical community while we’re building the telescope.
The James Webb Space Telescope — we’re building it as the successor to the Hubble Space Telescope, which has been in space for 26 years. Pretty incredible! Hubble was launched when I was in elementary school. And Hubble has obviously been instrumental in helping us learn about the universe. It’s completely changed, in fundamental ways, how we understand how the universe works. [But] there’s a lot of ways in which we’ve pushed Hubble to its limits, and so we’re designing Webb to answer some of the biggest questions in astronomy today that Hubble just can’t quite answer. All said and done, Webb will be something like 100 times more powerful than Hubble.
That’s sort of a broad way to say it, but what I mean by that is taking into account the size of the mirror. As you know, the size of the mirror is really important for telescopes: It's important because of the amount of light you can collect — a mirror is a "light bucket" — and also because the bigger the mirror, the finer details you can see. The Webb mirror covers about seven times more area than Hubble.
Another factor that makes it more powerful than Hubble is the wavelength range in which Webb will observe the universe. Hubble’s primarily an optical telescope; Webb will be an infrared telescope.
There’s also just observatory efficiency. Hubble’s about 350 miles up and orbits the earth once every 96 minutes. So Hubble is in sunlight half the time. It can only see the sky half the time, roughly. Webb, we’re putting out into deep space, so it’ll be about a million miles from Earth, and it’ll orbit the Sun along with the Earth. From that vantage point it’ll basically be able to work 24/7. So it’s a lot more efficient.
I read that the telescope will be placed at a Lagrange point. Can you explain the significance of that?
Yep. It’ll be at the second Lagrange point, or L2 as we call it.
LAGRANGE POINTS: This diagram shows the Lagrange points in the Sun-Earth gravity system (not shown to scale). The JWST will be parked at L2
In the most general question, the Lagrange points are different points in the Earth-Sun gravity system that are stable or semi-stable. You can park a spaceship at one of these places and it’ll sort of stay there, relatively speaking. L2 is a semi-stable point — like balancing a pencil upright on a table: If you don’t touch it, it’ll stay there but if you perturb it, it will fall. L2 is about 4 times further away than the moon.
You have these theoretical mathematical points in space where the gravity system gives you stability. There are 5 such points. L1 is between the earth and the sun, so that’s where NASA puts a lot of their solar satellites — the Solar and Heliospheric Observatory, for example [which is a joint project of NASA and the European Space Agency, or ESA].*
There are also two Lagrange points [L4 and L5] on Earth’s orbit around the sun, trailing and leading. The last point, or L3, is where Planet X would be [on the opposite side of the Sun from the Earth]. Don’t quote me on that! [laughs]
[Ed. note: To even vaguely grasp how Lagrange points work, I needed to see a demonstration of bodies in motion. This animation gives a good sense of the mechanics at play, although it shows the the Earth-Moon gravity system, rather than the Sun-Earth gravity system. Note that the point labeled L2 in this animation remains stationary relative to the moon's position as it revolves around the Earth. Similarly, L2 in the Sun-Earth gravity system remains stationary relative to the Earth's position as it revolves around the Sun.]
Have we ever parked anything at L2 before?
Yes. NASA and ESA, we’ve put things in that part of space before. That’s not the big technical challenge.
OK — so what are the big technical challenges?
This is an infrared telescope, so the telescope itself has to be very, very cold. That’s why we’re putting it in deep space. Things at room temperature glow in infrared. If we had our telescope in near-earth orbit, it would glow and the telescope would see itself, essentially. If you put a telescope out in deep space, the telescope itself cools: That’s a cryogenic telescope.
Another one of the big challenges — Webb is by far the biggest telescope we have sent out into space.
The biggest structure on the telescope is a giant sunshield — it’s about the size of a tennis court.
[Ed. note: As its name implies, the sunshield will shade the telescope from solar radiation. Being in deep space, far from the shadow of any planet or other body, the JWST will be continually exposed to sunlight. To keep its cryogenic instruments cool, the device must therefore create a shadow of its own. The sunshield will keep the telescope at a frigid -388 degrees Fahrenheit, while the side exposed to the sun will roast at around 185 degrees Fahrenheit. Here’s an explanation of why such temperature extremes occur in space in such close proximity.]
MOCK UP: This full-scale model of the JWST gives a sense of its size and shape.
From top to bottom, [the telescope] is between three and four stories tall. So the spacecraft itself is huge, and if you think about launching something that big into space — we don’t have any rockets that can launch something of that size fully deployed. The whole telescope has to fold up: Fold it up, pack it up, put it inside the rocket. Then it unfolds once it’s in space.
It takes about a month to get to L2, and several more months to settle into its orbit and do all the calibrations and checkups, etc.
The engineering behind creating a deployable, cryogenic telescope is extremely challenging. As an astrophysicist, I’m super excited about the data we’ll get. But one of the most fun parts of my job here at NASA has been seeing the engineering happen in real time: Talking to the engineers, learning about problems and issues that come up in building something like this, and seeing the process that they go through in working out those issues. I mean, this is really, really cutting-edge engineering, and it’s really, REALLY difficult.
Let’s talk about the science. You said Hubble has fundamentally changed our conception of the universe. How? If you were starting out pre-Hubble as an astrophysicist, how would your assumptions about the universe be different?
There are a whole lot of things. One of the coolest things that Hubble has done is show us things we didn’t expect. You know, when we set out to build telescopes like this, we have a set list of questions we want to answer. Every 10 years, astronomers get together and say ‘OK, let’s prioritize our top questions.’ And then they give that set of questions to the engineers and say, ‘Hey, build us something that will do this.’ Those are called decadal surveys. The mission that came from the 2000 decadal survey was the James Webb Space Telescope.
We have these big questions that define the mission, and we almost certainly will answer those questions or make really great progress on those questions. But the really cool thing that happens with these huge missions is that we also get surprised by the things we discover.
With Hubble, an example of that is dark energy. Dark energy is this mysterious force in the universe that is causing the universe to accelerate. This was discovered in the late '90s, and it was a complete surprise. We astronomers knew the universe was expanding, and we had the Big Bang to explain why the universe is expanding, and we thought either it’s going to keep expanding forever and slow down — the “Big Freeze” — or it will eventually slow down, stop and contract back into itself — the “Big Crunch.” But what we found instead, when we looked at the data, was that neither of these scenarios were happening. Instead, it was not only expanding but accelerating — expanding faster and faster all the time. This acceleration and expansion, we call dark energy. Astronomers have this annoying habit of calling anything we don’t understand ‘dark.’ [laughs] So we have dark energy to go along with dark matter, which combined makes up a huge fraction of all of the universe.
OLD FAITHFUL: The Hubble Space Telescope, shown here in a 2002 photo, is still operational today.
And we still don’t know what that is or where it is?
That’s right. Dark matter, we’ve made some progress on but still don’t know where it is; dark energy is still a pretty big mystery.
And will Webb explain what dark energy is?
Webb will definitely answer some questions about dark matter. Dark energy as well, in that we can refine some of our measurements. The way we discovered dark energy was to examine the brightness of supernova — basically, exploded stars — at different distances, and because supernovae are what we call ‘standard candles’ in astronomy, [they are the] same brightness when you look at them at different distances and therefore you can see how far away they are. So basically, the galaxies [we observed that contained those supernovae were] more distant than we expected them to be. And that’s what told us something weird was going on here and the universe was actually accelerating.
But we actually have another mission, the next big, big mission: “WFIRST.” That mission is specifically geared to study dark energy and exoplanets [which are planets orbiting stars other than the Sun]. But that’s fairly new; we only officially entered the NASA mission stage this year. Most people haven’t heard of it yet, but it’s the next big astrophysics mission. WFIRST is not as big or expensive of a mission [as Webb], so we hope to launch it in the 2020s. Because Webb is so big and so complex, it has taken decades to build this telescope.
One of the interesting things about NASA is that people sometimes spend their whole career working on one mission. People started thinking about the successor to Hubble in the mid-'90s, shortly after Hubble was launched. So, decades of work go into defining and then building and operating the mission.
If you’re putting Webb four times farther than the moon, will there be any way to do repairs if need be?
We are not building Webb to be serviceable. The idea of getting humans out that far is pretty far-fetched right now. Naturally, when people think of Hubble, they think of the fact that astronauts have serviced it, and that’s possible because Hubble is relatively close, in low-earth orbit. But Hubble was the exception to the rule. Hubble is the only spacecraft we’ve been to, besides the space station, that human beings have [serviced in space].
Astronauts have been to Hubble five times — replacing batteries, replacing gyroscopes, replacing circuit boards on instruments that fail. But Hubble was designed to be that way — modular, serviceable, its instruments designed so they could be slid in and out. Webb is definitely not designed that way, which is one of the things that makes it a little bit, ah, high-pressure.
It’s extremely complex, it’s the largest space observatory we’ve ever built, and it has to work once it gets into space.
But I guess that’s usually the case when NASA launches an extraplanetary mission to Mars or Jupiter or wherever — once it’s gone, it’s gone.
Exactly. Space is hard. It always is.
Every time we launch something, there’s absolutely a chance it won’t work, because space is hard and it always will be.
You mentioned exoplanets earlier, or planets that orbit other stars besides the Sun. We know they're there, but we don't know much about these other worlds. Will Webb be studying planets outside of the solar system?
Absolutely. When we first started developing this telescope [in the '90s], we didn’t know of any exoplanets — but it turns out the technology we developed for Webb is going to be awesome at discovering exoplanets.
Thanks to NASA’s Kepler telescope, we now know that exoplanets are everywhere, and that’s such a fundamental paradigm shift in how we think about the universe. When I was a kid, we only knew of the nine planets in our solar system. [laughs] Well, no longer nine, but …
Now, we know that [planets] are everywhere. There are statistically probably more planets in our galaxy than stars. And that’s mind-blowing. That’s completely — no one expected that. But that’s one of the cool things about launching these awesome telescopes. Kepler is a relatively small telescope, dedicated [to a single, narrow mission of planet hunting.] What it does is looks at one patch of the sky and watches for transits, watches for when planets are crossing in front of their stars. But just that small, simple telescope has fundamentally changed the way we understand the universe.
So Kepler watches for those transits and shows us the planets are there — but it’s not really able to focus in and study the planets in detail. Webb will be able to do that. What we want to do is watch planets pass in front of their star. We look at the starlight that is passing through the atmosphere and coming towards us, coming towards our detectors. You can imagine how difficult that gets, because stars are bright, planets are tiny and their atmospheres are minuscule. That’s such a technological challenge. But with Webb, we have this huge mirror and these ultra-sensitive detectors [and] we expect to be able to do transit spectroscopy in a new way.
ESA / HUBBLE VIA WIIPEDIA
PROXIMA CENTAURI: The Sun's closest stellar neighbor has at least one planet of its own.
Spectroscopy? So you’ll be able to analyze the chemical composition of an exoplanet's atmosphere based on the light filtering through it?
That’s right. Webb would able to detect, for example, water vapor in sort of a super-Earth-sized planet around a nearby star. It probably wouldn’t be able to get down to small, rocky planets unless we get really, really lucky. But I believe Webb is the next big step in our understanding of exoplanets.
If you’re an astronomy enthusiast, you’ve probably heard of Proxima b? We definitely should be able to study that planet.
[Ed. note: In August, an international team of scientists announced they had confirmed the existence of a planet orbiting the red dwarf star Proxima Centauri, which is the closest star to the Sun — just four light years away. What's more, the exoplanet's orbit around its parent star falls within the 'Goldilocks zone' — that is, with sufficient atmospheric pressure, its estimated temperatures could possibly support liquid water, although it may well be uninhabitable for other reasons.]
Really — even though the star is so dim?
There was actually a paper that came out on it soon after [the discovery of Proxima b], saying ‘Given the parameters that Webb has, we should be able to do some studies on it.’
Exoplanet research is fairly far removed from my own personal area of research, but I really think it’s going to be one of the most exciting things that Webb does.
Your own research concerns galaxy formation — tell me about that.
I’m really interested in the big picture of how galaxies change over time. If you think about galaxies in the nearby universe, they fall into two broad categories — they tend to be either disc shaped — spirals — or elliptical, big balls of stars. But if you start looking into the distant universe, you see a different picture. You see galaxies that are oftentimes more clumpy. They don’t have the same organized structure that you see in the nearby universe. So I’m interested in how galaxies change over time, how they form their stars and how they form their black holes.
NASA / ESA
HOSTILE TAKEOVER: The galaxy NGC 6052, located about 230 million light years away, is thought to be the product of a collision between two smaller galaxies.
Do galaxies come and go, then? I think of them as being as old as the universe itself.
The processes that happen in galaxies obviously take place over billions of years. So, how do we know what’s going on? I’m really interested in the process that galaxy mergers play in the overall evolution of galaxies, but because they take billions of years to happen, how do we see it happen?
The answer is that we do it statistically. So, we look at these huge swathes of sky and look for galaxies in different stages of mergers. So maybe, two galaxies that are close together but don’t have any distorted shapes yet. And then, galaxies that have gotten close enough that you can tell they’re interacting — they have these tidal arms and bridges and maybe their black holes are starting to light up. So, you can tell that they’re interacting.
Starting to light up?
One of the cool things that we think might happen in galaxy mergers is that the gas gets stirred up and funneled to the inside, and the black holes become active. We call that an AGN — an ‘active galactic nucleus.’ And so, yeah — the black holes become active and have an accretion disc around them, and those glow and shine really brightly. So that’s what a quasar is. The galaxy is dynamic and the black hole has developed a huge accretion disc around it, so it’s actively accreting material.
The way astronomers think about this changes as we get new data. But we think that these galaxy mergers may be one way that galaxies grow over time. And it also may be how elliptical galaxies form — those balls of gas that don’t have the spiral structure, those might have been formed from galaxy mergers. ...
NASA / ESA
THE ANCIENTS: A portion of the Hubble Ultra Deep Field image shows a riot of galaxies in the early universe.
One of the things that Hubble has given us is the Deep Field images. I did my dissertation work on the Hubble Ultra Deep Field, which came out I believe in 2003.
[Ed. note: The Hubble Ultra-Deep Field is an image that was created by aiming the telescope at a section of the sky with a low density of relatively nearby stars, thus allowing the telescope to peer as far into intergalactic space as possible. Hubble collected data for several months, which was then composited into a picture of the most distant — and therefore earliest — slice of the universe the human species has yet seen. The Ultra-Deep Field image is a glimpse some 13 billion years back in time, less than 1 billion years after the Big Bang itself.]
You look at that image, and it’s readily apparent that galaxies come in all different shapes and sizes and colors. The galaxies in the early universe, in the distant universe, are very different from the ones we see nearby. But there’s a lot we just don’t know yet. For example, when we look in the distant, early universe, we see galaxies that are huge, and we don’t have a great idea of how they got so big so fast. Also, every large galaxy in the nearby universe has a huge black hole in the center — sometimes many billions of times the mass of the sun. These monster black holes at the center of galaxies — we don’t really know how they got so big.
One of the fun things about being an astronomer is that we’ve learned so much using the telescopes, in space and on the ground — but there’s still so much we don’t know yet. We’re never going to run out of questions to ask and things to look for.
*Correction, 10/25/2016: This sentence originally said the solar satellite at the L1 point was NASA's Solar Dynamics Observatory, or SDO. It is in fact SOHO, which is a joint project of NASA and the ESA.