by Erik Pena
With the exciting launch of the James Webb Space Telescope (JWST) back on December 25, 2021, new and beautiful images have been taken of the universe in greater detail than ever before (Figure 1). The universe is riddled with stars, galaxies, black holes, and planets just waiting to be explored and studied. In order to study more of the universe and all its mysteries, the JWST is packed with new technology to photograph distant objects in the sky in high detail. Scientists can now take images of newly discovered stars and learn about the chemistry of different planets. However, taking nice photos is not the only mission this telescope is being used for. One of the most important missions it is tasked with is taking images of the universe’s past. Roughly 13.5 billion years in the past! With this, we can begin to research and truly understand what galaxies and black holes were doing during the early years of the universe.
Figure 1. High resolution image of the Carina nebula taken from the James Webb telescope. A nebula is a large cloud of gas and dust that looks like mist in the spaces between stars.
How exactly does the JWST take images of the universe so far into the past? To begin understanding how this is accomplished, you must first understand that light traveling through space is not instantaneous. Light is the fastest moving object in the universe (approximately 300,000,000 meters per second). However, it still takes time to travel through the vastness of space. For example, if you were to look at our sun (do not do this without protective equipment!) that is 93 million miles away from the earth, it would take 8.3 minutes for the light from the sun to reach your eyes. This means you are watching the sun that is 8.3 minutes in the past! Therefore, the further away a planet, star, or galaxy is from Earth, the further back in time we can see.
But any old telescope can look at distant stars, what makes the JWST so special? What makes it special is that it is equipped with two infrared-sensing detectors. Infrared light is not visible to the human eye, but we can feel it as heat. Through ingenious engineering, the JWST can focus light using several large beryllium mirrors that are coated with gold (Figure 2). Beryllium is used as the mirror’s internal structure because it is incredibly lightweight and is able to hold its shape against the extreme temperatures of space. The gold is used to coat the mirrors because it is highly reflective to infrared light, allowing it to focus the light more efficiently. The telescope is so sensitive to infrared light, that it is said that it can detect a bumblebee’s heat all the way from the moon.
Figure 2. An image of the James Webb Space Telescope (JWST) where 18 hexagonal, gold-coated beryllium mirrors are used to focus light to achieve high infrared detection sensitivity. Image source.
Okay, so the JWST is highly sensitive to infrared light. How does this help look at far away stars and galaxies? Well as it turns out, the universe is expanding. As light travels through space, the expansion of the universe stretches out the short wavelengths of visible light into longer wavelengths of light. This is a process called redshift (Figure 3). Therefore, the light that is emitted from distant stars or galaxies is being redshifted into the infrared spectrum.The JWST can detect these wavelengths with incredible sensitivity. Furthermore, infrared light can pass through dust clouds and regions of gas that may otherwise block or scatter visible light. This allows infrared light to hold a magnitude of information about galaxies and stars that are tremendously far away that visible light simply cannot do.
Figure 3. Illustration of visible light wavelengths redshifting due to the distance the light travels and the expansion of the universe. Image source.
Through the detection of infrared light and the sensitivity of the JWST, far away galaxies and stars can now be made visible to us. Researchers are using this technology to understand the early universe by looking at infrared light that was emitted by galaxies 13.5 billion years ago that are just now making their way to Earth. Recently, the JWST imaged the furthest star, Earendel, and the light emitted from that star is estimated to be 12.9 billion years old! It is also estimated that the universe is about 13.8 billion years old. With JWST we can peek into the early stages of the universe, the formation of galaxies, the evolution of supermassive blackholes, and so much more.
