What the Webb Space Telescope Will Show Us Next

When the Hubble Space Telescope launched, we soon learned its images were blurry. Engineers had to build the equivalent of eyeglasses for it. Were there any such problems with J.W.S.T. early on, given its very complicated deployment?

Because of the way it worked, when Hubble went up in space, the optics had to be perfect. For J.W.S.T., we launched mirrors that were able to fix themselves. There are eighteen primary mirror segments—those beautiful gold hexagons—and the idea is that you design them to be correctable in space. You just move them until they’re in the right places. When J.W.S.T. first deployed, through this long, iterative process of looking at bright stars, we got all of those mirrors to work together like a chorus—where, at the beginning, everybody’s in their own key, their own song, their own genre, doing their own thing. And, at the end, they’re coördinated, singing in a tight, multipart harmony.

The real problem with J.W.S.T. was that we needed a telescope bigger than rockets are. The rocket we launched on is a little more than five metres across. But just the telescope part of J.W.S.T. is 6.6 metres across (and then there’s this whole sunshield underneath it that’s the size of a tennis court). One way to overcome the size limit, which is a fundamental challenge for space telescopes, is to have them fold up. Six of the primary mirror segments were tucked back behind the rest of the mirrors for launch. Then they unfolded on hinges. So that led to a design where we didn’t need to align them perfectly on the ground.

If size is but one challenge for space telescopes, what you would say is the greatest one?

Oh, my gosh. I think, right now, the greatest challenge is just time. The telescope is about one hundred times more powerful than anything we’ve had before. In the same observing time, it can see things that are a hundred times fainter than we could see with Hubble or with the Spitzer Space Telescope. So it is this powerful beast, and, in the first year of science operations, we have about five hundred different observing programs—in total, thousands of people from all over the world—who are using this telescope.

In a given day, we will observe a quasar, which is an accreting black hole that is as far away as we can see, and then, a couple of hours later, we’ll go observe an asteroid in our own solar system. Then we might go observe a nearby galaxy. We have a schedule, and we are doing observations that were selected competitively by the scientific community as the most compelling. And we are doing observation after observation, and then getting those data out to the world. The ingredient for discovery is just time.

What are the main questions J.W.S.T. must answer for this mission to have been considered a success?

Well, it’s worth taking a moment to go back a bit. Hubble launched in 1990, and there were three key questions that it set out to answer. One was: How old is the universe? Which is really a measurement about how fast the universe is expanding. We now know that that wasn’t the most exciting question to ask. In the course of measuring that expansion of the universe, astronomers came to understand that the universe’s expansion is accelerating. That was the unexpected discovery.

The second one was: What are quasars, and what is their relationship to galaxies? Well, from work with many telescopes, including Hubble, we now know that quasars are supermassive black holes of a million to a billion solar masses in the hearts of galaxies that are fuelling—that is, they are feeding on gas, and even destroying stars—and, in doing so, are shining as bright or brighter than their parent galaxies. We know that every galaxy has such a black hole in its heart but that most of them are asleep. A small fraction of them, however, are turned on and are fuelling. We don’t really understand how the black holes and their parent galaxies evolve together. We have evidence that one’s controlling the other, but we don’t know how.

Third, Hubble was also built to study the gas between galaxies. And we now understand that galaxies are constantly being fed by this web of gas that links galaxies together—like, this structure spanning the void with a beautiful kind of filamentary geometry. And we know that how galaxies are connected to that network determines how they’re able to fuel and grow. It’s fun to think back over thirty years and realize how little we understood thirty years ago, and how far we’ve come.

What about J.W.S.T.?

For J.W.S.T., the questions that we knew we were going to ask were: What did the first billion years look like? How did galaxies get started? From the data we have so far, we’re going to do a great job on that question. We are finding galaxies further back than we knew were possible. We’re seeing back in time to about three hundred million years after the Big Bang. The elevator pitch we used when J.W.S.T. was sold was that we’ll see the baby pictures of the universe. And we will definitely do that.

J.W.S.T. was also built to study the atmospheres of planets orbiting other stars. That’s the other really high-profile science case. And we’re doing that, but we haven’t gotten far enough yet during our first year of science observations.

What gaps in science do the J.W.S.T.’s unique capabilities fill?

J.W.S.T. works in the infrared. It was designed to see the light from the universe that is totally invisible to Hubble, which sees primarily in the optical and ultraviolet. About the “bluest” light that J.W.S.T. can see is the shade of red wine, and then it goes redder from there.

Because of the Big Bang, space is expanding—not just stuff in space but the fabric of space itself. And the light that we see from distant objects has actually been stretched by the expansion of the universe as well. That causes light from those distant objects to get stretched to longer wavelengths. It gets shifted to the red, to lower energies.

It’s just really cool that we can see almost to the end of the universe, right? We can do that because that light only travels so fast: the speed of light. We are studying galaxies whose light has been travelling for more than thirteen billion years. The universe is only about 13.8 billion years old! Those are the baby pictures of literally everything, and, in particular, of the baby galaxies that would have turned into mature galaxies like our Milky Way.

Why else does J.W.S.T. need to see in the infrared?

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