Imagine such a powerful camera that you can see the light of the galaxies that were formed more than 13,000 million years ago. That is exactly what the NASA James Webb space telescope is built.
Since its launch in December 2021, Webb has been orbiting more than one million miles from the earth, capturing impressive images of deep space. But how really does it work? And how can you see until now? The secret is in its powerful cameras, especially those that do not see the light as our eyes do.
I am a astrophysician who studies galaxies and supermassive black holes, and the Webb Telescope is an incredible tool to observe some of the first black galaxies and holes in the universe.
When Webb takes a photo of a distant galaxy, astronomers like me are seeing what that galaxy was billions of years ago. The light of that galaxy has been traveling through space during the billions of years that takes to reach the telescope mirror. It is like having a time machine that takes snapshots from the primitive universe.
Through the use of a giant mirror to collect ancient light, Webb has been discovering new secrets about the universe.
A telescope that ‘sees’ heat
Unlike normal cameras or even Hubble space telescope, which take images of visible light, Webb is designed to see a type of light that is invisible to the eyes: infrared light. Infrared light has longer wavelength than visible light, so our eyes cannot detect it. But with the right instruments, Webb can capture infrared light to study some of the oldest and most distant objects in the universe.
Although the human eye cannot see it, people can detect infrared light as a heat form using specialized technology, such as infrared cameras or thermal sensors. For example, night vision glasses use infrared light to detect hot objects in the dark. Webb uses the same idea to study stars, galaxies and planets.
Why infrared? When the visible light of distant galaxies travels through the universe, it stretches. This is because the universe is expanding. That stretch turns visible light into infrared light. Therefore, the most distant galaxies in space no longer shine in visible light, but in dim infrared. That is the light that Webb is designed to detect.
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A golden mirror to collect the most dim gum
Before the light reaches the cameras, it must first be collected by the huge golden mirror of the Webb Telescope. This mirror has more than 21 feet (6.5 meters) wide and is made of 18 smaller mirror pieces that fit like a honeycomb. It is covered with a thin layer of authentic gold, not only to look elegant, but because gold reflects infrared light very well.
The mirror collects the light of deep space and reflects it in the instruments of the telescope. The bigger the mirror, the more light can collect and the further you can see. Webb’s mirror is ever released into space.
Inside the cameras: Nircam and Miri
The most important “eyes” of the telescope are two scientific instruments that act as cameras: Nircam and Miri.
NIRCAM are the acronym for the near infrared chamber. It is the main camera of the Webb and takes impressive images of galaxies and stars. It also has a coronograph, a device that blocks the light of the stars so that it can photograph very weak objects near bright sources, such as planets that orbit bright stars.
Nircam works by obtaining images of the near infrared light, the closest type to what human eyes can almost see, and dividing it into different wavelengths. This helps scientists learn not only how something looks like, but what is done. Different materials in space absorb and emit infrared light in specific wavelengths, creating a kind of unique chemical fingerprint. When studying these fingerprints, scientists can discover the properties of distant stars and galaxies.
Miri, or the medium infrared instrument, detects longer infrared wavelengths, which are especially useful for detecting colder and dusty objects, such as stars that are still being formed inside gas clouds. Miri can even help find clues about the types of molecules in the atmospheres of the planets that could house life.
Both cameras are much more sensitive than standard cameras that are used on Earth. Nircam and Miri can detect the smallest amounts of heat to billions of light years away. If you had the Nircam on Webb as eyes, you could see the heat of a bark on the moon. That is how sensitive it is.
Because Webb is trying to detect the faint heat of distant objects, you need to stay as cold as possible. That is why he carries a giant parasol the size of a tennis court. This five -layer sunscreen blocks the heat of the sun, the earth and even the moon, which helps Webb to stay incredibly cold: around -370 degrees F (-223 degrees c).
Miri needs to be even colder. It has its own special refrigerator, called cryogenic refrigerator, to keep it cold at almost -447 degrees F (-266 degrees c). If Webb were a little hot, its own heat would drown the distant signals that you are trying to detect.
Convert the light of space into images
Once the light reaches the cameras of the Webb Telescope, it reaches sensors called detectors. These detectors do not capture normal photos such as the camera of a phone. Instead, they turn incoming infrared light into digital data. Then, these data are sent to the Earth, where scientists process them in full color images.
The colors we see in Webb photos are not what the camera “sees” directly. Because infrared light is invisible, scientists assign colors at different wavelengths to help us understand what is in the image. These processed images help to show the structure, age and composition of galaxies, stars and more.
Through the use of a giant mirror to collect invisible infrared light and send it to super cold cameras, Webb allows us to see galaxies that formed just after the universe began.
*Adi Ford is an assistant professor of Astronomy and Astrophysics at the University of Maryland.
This article was originally published in The Conversation/Reuters
