Mint Explainer: How James Webb Shoots Through Cosmic Dust

But if you are a professional photographer, the dust in your sensor will block the light from reaching that specific area of ​​your camera. As a result, pixels in that area will appear as dark spots in photos. This is the reason why professional photographers take great care when shooting in dusty places. But even they can always clean the lens as the camera is in their hand or within reach.

But what about giant telescopes like the James Webb Space Telescope (JWST), which are orbiting in space to take pictures of the early universe, not on the ground?

For example, Hubble is in low-Earth orbit which is located about 375 miles (600 km) from Earth while Webb is being operated about 1 million miles (1.5 million km) from Earth. So how do these cameras see the dust in space, and how do these lenses stay clean even when they are millions of miles from Earth?

To begin with, JSWT uses infrared cameras to see through interstellar dust. This is similar to how firefighters use infrared cameras to see through smoke in a fire and save people, or how forest officials use night-vision goggles to find animals. Of course, this is done on an unimaginably exponential scale.

But what are infrared waves or infrared light?

Almost all TV remotes use near-infrared (near-, mid- and far-infrared are terms) to allow you to switch channels. Near-infrared is that part of the radiation that is just beyond the visible spectrum. For example, scientists can also study vegetation from space using reflected near-infrared radiation that can be sensed by satellites.

Infrared itself is part of the electromagnetic (EM) spectrum that the human eye cannot see but detects as heat. The EM spectrum includes (in order of highest to lowest): gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. Gamma rays have the highest energy, shortest wavelength and highest frequencies in the EM spectrum. Radio waves rank lowest in order.

To be sure, all electromagnetic radiation is light in origin but we can only see a small part of this radiation which we call visible light. However, visible light (which we humans rely on) cannot detect very cold and faint objects in the universe such as planets, cold stars and nebulae. Therefore, astronomers use infrared light as it penetrates dust clouds (the stars and planets form inside those dust clouds) compared to visible light.

In addition, since infrared waves have a longer wavelength than visible light and can pass through dense regions of gas and dust in space with less scattering and absorption, they are used to reveal objects in the universe. which cannot be seen in visible light using optical telescopes. Dense gas clouds block their light.

In addition, objects that have a temperature similar to Earth’s emit most of their radiation at mid-infrared wavelengths. These temperatures are also found in dusty regions, from which stars and planets are formed. Therefore, mid-infrared radiation allows scientists to see the star’s brightness and planet formation with the help of an infrared-adapted telescope.

In addition, as the universe is expanding, we encounter redshifting, which means that the light that is emitted as ultraviolet or visible light is at greater redder wavelengths, near and middle of the light spectrum. – gets transferred to the infrared part.

shine more light on mirrors

As you may have realized by now, JWST uses infrared instruments to observe past cosmic dust and helps scientists study the origins of the universe and the formation of galaxies, stars and planets. That said, the sensitivity (details it can see) of a telescope is also directly related to the size of the mirror sphere that collects light from objects.

JSWT’s primary mirror is much larger than Hubble’s (2.7 times larger in diameter, or about six times larger in area), allowing it to collect more light. According to NASA, its infrared instruments also have significantly improved longer wavelength coverage and sensitivity than Hubble.

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JSWT’s mirrors (18 hexagonal-shaped mirror segments made of beryllium that are lightweight and stable at cold temperatures. The segments were designed to fit into rockets and appear in space) also adapted for infrared light To be coated with gold. Which later absorbs blue light but reflects yellow and red visible light. The gold is also coated with a thin layer of amorphous SiO2, ie glass, for protection.

But infrared light posed another problem. The mirrors would need to be super cooled (about -240 degrees centigrade) in deep space to avoid an infrared glow (since hot objects emit infrared light), which can blind the faint infrared light from distant galaxies and may spoil the images.

And, of course, JSWT uses a high-frequency radio transmitter to transmit all this data at 28 Mbps – about 57GB of data per day. An Artificial Intelligence (AI)-powered model called Morpheus has been trained on UC Santa Cruz’s LUX supercomputer (which consists of 28 GPUs (Graphic Processing Units), each consisting of two NVIDIA V100 Tensor Core GPUs). The machine will help scientists decode full-color images from the $10 billion space telescope.https://webb.nasa.gov/,

Finally, how does NASA keep mirrors stable and clean in space?

Before launching on an Ariane 5 rocket on December 25, 2021, the James Webb Space Telescope underwent months of commissioning, ensuring that its mirrors were aligned, and its instruments were calibrated in its space environment. Other than that there was no contamination by the special wrapping. mobile clean room (https://www.nasa.gov/feature/goddard/2018/nasas-webb-telescope-wrapped-in-a-mobile-clean-room) The glass of the web was also polished to an accuracy of less than a millionth of an inch. It is important to get the sharpest images possible when the mirror cools down to -400°F (-240°C) in deep space.

In addition, JSWT is being protected from external sources of light and heat (such as the Sun, Earth, and Moon), as well as heat emitted by the observatory, with a five-layer, tennis court-shaped sunshield made of a material called Kapton. is made from. Which was developed by DuPont in the late 1960s. NASA likens the sunshield to an umbrella providing shade that will keep infrared cameras and instruments too cold and away from the sun’s heat and light so that they can function properly.

Given the harsh conditions in space, JSWT does not use conventional cameras that explode in space or interfere with its extremely sensitive equipment. That’s why all of JSWT’s systems—Near Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS-NIRISS)— Contained in an Integrated Science Instrument Module (ISIM) and also designed to survive micrometeoroid hits.

While NIRCam will be able to detect extremely distant objects, MIRI will help scientists confirm whether these faint sources of light are actually first-generation stars or second-generation clusters that later evolved into a galaxy. There are. Since MIRI can see even through denser clouds of dust than NIRCam, it will also detect molecules that are common on Earth such as water, carbon dioxide and methane.

NIRCAM is equipped with coronagraphs that allow astronomers to take pictures of very faint objects around a centrally bright object, like stellar systems. They are expected to help astronomers determine the characteristics of planets orbiting nearby stars. You can find technical details here Science Tools (stsci.edu),

MIRI has both a camera and a spectrograph that observes light in the mid-infrared region of the electromagnetic spectrum as described in the earlier paragraphs.

The sunshield would allow the telescope to cool to temperatures below 50 Kelvin (-370 °F, or -223 °C) by passively radiating its heat into space. The near-infrared instrument (NIRCam, NIRSpec, FGS/NIRISS) will operate at approximately 39 K (-389°F, -234°C) via a passive cooling system. The Mid-Infrared Instrument (MIRI) will operate at a temperature of 7 K (-447°F, -266°C) using a helium refrigerator or cryocooler system. The sunshield also provides a thermally-stable environment that is necessary to maintain proper alignment of the primary mirror segments as the telescope changes its orientation to the Sun.

But before we finish, it’s important to note that the full-color images Webb reported on July 12 this year were “synthetic” (known as “false colors”), but they were fake images. Because telescopes record images in black and in black. White through color filters that are used to record specific wavelengths of light. Scientists use different wavelengths to give us those brilliant color images. Combine the multiple shots of the same field obtained at the same wavelength. We can only wait for more breathtaking images from JSWT.

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