Inventing ways to see deeper into space than ever before
These are some of the newest and best pictures we have of our universe, taken by the James Webb Space Telescope (JWST for short).
Images taken by JWST of the galactic Deep Field, the Cosmic Cliffs of the Carina Nebula, and the Southern Ring Nebula. Courtesy of NASA.
The camera that’s on the JWST lets us see our universe more clearly than ever before. That camera is called the NIRCam, and it was developed by a team led by an astrophysicist named Marcia Rieke. Thanks to Dr. Rieke’s work, we’re making new discoveries about our universe just by looking at it a little bit closer.
Lifelong love of the stars
Marcia Rieke has been in love with the stars her whole life. As a kid, she checked out books on astronomy from her public library, and devoured sci-fi stories about humans in outer space. When she was in high school, she saved up enough money by babysitting to buy her very own telescope. It might have been those stories about space explorers, but when Marcia started college, her dream was to be an astronaut. She quickly realized that her passion instead lay with astrophysics - the physical laws that govern how the stars and galaxies move, form, and evolve. Marcia got her PhD in physics from MIT, and eventually became a professor at the University of Arizona.
At the university, Dr. Rieke started working with a group of scientists to design special telescope cameras that see in the infrared region of light. Over the course of her career, she’s become one of the leading experts on these kinds of cameras. She’s worked on several NASA telescopes, including the Hubble Space Telescope, and most recently, was the lead scientist that developed the NIRCam for JWST. Dr. Rieke led the project to build a state-of-the-art camera that would be launched into space, travel a million miles away, and take crisp, precise photographs of millions of faint stars and galaxies.
That sounds like a tough project! But how does a space telescope like JWST even work?
JWST and other telescopes like it work by collecting light with mirrors. When you look in a mirror, you’re seeing the light that is bouncing off your face, hitting the mirror, and bouncing back into your eyes. In a way, telescopes are like giant, robotic eyes, trying to pick up light that’s reflected by a mirror. On the JWST, there’s a 21 foot (6.5 meters) mirror that’s coated with gold. This mirror was too big to launch into space directly, so instead it’s made up of many hexagonal pieces that all fit together. It’s also curved like a Pringle, so that when light hits the mirror, it bounces inward to a point in the middle. There, another (much smaller) mirror bounces the light through a small hole to the inside of the telescope. The light can then be directed onto many sensitive cameras and instruments.
Light is a spectrum. It comes in lots of different forms that depend on its energy. Light that is very high energy, like Gamma rays or X rays, has a very short wavelength. That short wavelength means that it oscillates very quickly, which we call having a high frequency. On the other end of the spectrum is light that has a low energy, like radio waves or microwaves. These waves have super long wavelengths, and oscillate at a much lower frequency. Humans can only see light in a narrow range of wavelengths (called visible light), but we can make instruments that detect light that’s too high energy or too low energy for our eyes to see.
This is super useful because not everything emits light with the same energy. For example, our Sun emits most of its light in the visible spectrum, but stars that are very hot and very big emit more in the ultraviolet (UV) range of the spectrum. On the other hand, stars that are very old and very cool emit more in the lower wavelength infrared (IR) spectrum. What’s more, when objects are very far away, the light stretches out as it comes to us, getting longer and longer wavelengths. These old stars and galaxies are typically very faint, and they’re what we’re trying to see with JWST: the most distant and oldest objects in the Universe.
Now that we know how telescopes work, what about the cameras?
Light is made up of particles called photons. Cameras work by directing the photons to a sensor that counts them. This sensor is usually made up of semiconducting material like silicon divided up into millions of equal sized pixels. We can think of pixels as tiny buckets. As the photons ‘rain’ down on the sensor, they fall into these buckets and are turned into electrons. The camera then counts how many electrons are in each bucket. The pixels with more electrons are made brighter, and the pixels that have less are made dimmer. These pixels are all pieced together to form an image of what the camera was pointed at.
NIRcam: a super special camera
The NIRcam that Marcia Rieke designed works the same way - it turns photons into electrons and collects them in buckets. Each detector in NIRCam has 4 million pixels. But NIRcam needed to be a bit more complex in order to meet the needs of the scientists. They needed the camera to be able to do several things:
Observe super faint objects.
Produce high resolution images, but also keep the longer wavelength information
Keep the camera cool enough to be able to detect faint objects
In order to see the faintest objects in the Universe (like exoplanets or old stars), you need a really big telescope with really precise instruments. But even with those, there’s still a big obstacle to seeing faint signals: the Sun.
Our star is by far the brightest object in our sky. If NIRCam were to take a picture of any part of the sky (even facing away from the Sun), the light from the Sun would overwhelm all other light. If you’ve ever had to look in the direction of the Sun and had to shield your eyes to see, you’re experiencing a similar effect to this!
Dr. Rieke and her team needed a way to turn off the Sun. Sounds impossible, right? But what they ended up designing is something called a coronagraph. A coronagraph blocks out light from a bright object so that it’s possible to separate the light from the faint stars and galaxies behind it. The NIRCam coronagraph can work on more than just our Sun, though. It has 5 possible shapes to block other objects too, like stars with planets around them that would be too dim to see otherwise.
The second important part of NIRCam is the beam splitter. The beam splitter works just like its name suggests - it splits the incoming beam of light in two. It’s made of a prism that’s coated with a special material that separates the light into longer and shorter wavelengths. Using the shorter wavelengths to make a picture gives you much more detail and resolution, but the longer wavelengths hold a lot of information about the object we’re looking at. By using the beam splitter, Dr. Rieke and her team designed a camera that could take sharp pictures but still preserve those important clues in the longer wavelength light.
The last challenge Dr. Rieke faced is making sure that the camera is cold enough to function properly. That’s right, COLD enough. The NIRCam needs to be about -288 degrees Fahrenheit (-178 C) to function properly. Why is that?
If you’ve ever used night-vision goggles, you’ll know that you can see people and animals glowing, even when you can’t see them with your naked eye. Those goggles are recording the world in the infrared range of light, which is given off by warm objects, like people! Astronomical objects like distant galaxies, stars hidden in cocoons of dust, and planets outside our solar system all emit infrared light, which NIRCam wants to detect. The problem is, the electronics inside the camera can also heat up and emit IR radiation (think of how a laptop gets hot when you’re playing video games). If NIRCam isn’t kept cool, it could detect its own radiation!
Dr. Rieke and her team addressed this problem by building their detector out of a special material called Mercury-Cadmium-Telluride (HgCdTe). Not only does this material make a great electron conductor, but it also doesn’t produce any extra radiation or signal if it’s kept under -393 F, which isn’t so hard to achieve in outer space where the average temperature is -455 F. The team could just let the material cool down naturally in space, and not have to worry about an additional cooling system.
A glimpse into the cosmos
The James Webb Space Telescope has been the culmination of over two decades of work and research. It was a long and expensive project, but we’re just starting to see the results of all that effort. Who knows what we’ll discover in the decades to come? It’s an exciting time for astronomers like Marcia Rieke. After years of developing the camera in the laboratory, her work is now a million miles away, happily taking pictures deeper and deeper into the cosmos.
Written by Lindsey Oberhelman
Edited by Caroline Martin
Sources and Additional Reading
Near Infrared Camera (NIRCam) by NASA
My NASA Experience by Marcia J. Rieke
Making a Camera That Works a Million Miles Away by Mark Stein
NIRCam Imaging by James Webb Space Telescope
Learning more about space telescopes and astronomy!
Watch (5 minutes): Watch this video to understand how astronomers get information from different wavelengths of light. The Whirlpool Galaxy is a beautiful spiral galaxy, and NASA has run missions to observe it with a whole bunch of different telescopes. See how much we can learn about the Whirlpool Galaxy by looking at it in infrared, visible, and X-ray light.
Explore (20 minutes): There are tons of beautiful images of our universe, taken at almost every wavelength of light you can imagine. But how do these wavelengths come together to make up an image? Check out this library of astronomical images to find out. You can search the site by filtering through what wavelengths make up the image. Can you find a picture made up of only one kind of light? What about one made up of two or three different kinds of light? How do pictures of the same object look different in radio waves vs. visible light? Go on a scavenger hunt and see what you can find!
Analyze (1 hour): Humans can only see the wavelengths of light that are in the visible spectrum. So how are we supposed to look at pictures of stars taken with IR, or even with X-rays? The answer is by using computer code to “recolor” the images to things that we can see. But this process can require a bit of an artistic eye. Try your hand at coloring a picture of our universe with coding by following along with this activity and tutorial. Don’t worry if you don’t have much experience with programming! This tutorial takes you through everything you need to know, while still giving you space to experiment and learn on your own.
Build (30 minutes): The James Webb Space Telescope is the latest of a long line of super cool space telescopes that we’ve launched into orbit. To learn how these telescopes are fit together, make your own models of them out of paper! These origami-inspired paper telescopes are educational and also pretty cute.