#6 A new eye on the Universe

Hi reader,

this article will make you stop thinking about your everyday problems and start looking a little higher, at the sky and the infinite space above us. Gaia Dimitri, Aerospacial Engineering student at the Politecnico of Turin, will transmit you her huge passion about this topic, revealing you the meaning of some of the most emblematic pictures of the Universe and the tools used to capture these works of art. Enjoy the reading!

It's really true that "the essential is invisible to the eyes". Antoine de Saint-Exupéry was talking about the human nature and the meaning of life, but it can be applied to science and, especially, to the study of the universe. Indeed, we have only known around the 4% of the matter of our universe so far, and the questions we still can't answer are infinite. It doesn't mean that we can't create tools capable of helping us see further, eyes more powerful than ours. This is the reason why the James Webb Space Telescope was born, launched in the space the 25th December 2021.

Designed in the middle '90s, it was thought as a science fiction project. Nevertheless, almost 20 years later, challenging countless mishaps, delays and accidents, the JWST has finally captured the first images of its long list of goals.

The first one, named by the astronomists "Webb's First Deep Field", represents SMACS 0723, a cluster of galaxies. A deep field is an image that needs a long exposition to capture the light coming from the innermost areas of the space, focusing on a small portion of sky. To understand how much it is, take a grain of sand and put it on your arm: all the stars and the galaxies in this first picture are in a fraction of sky as big as that grain.

The image is a composition of several overlapping shots, and the colours vary according to heat and distance of each corp. The luminous entities with the 6 big tips are stars, while the other are galaxies. These tips are a consequence of the interaction between the light of the star and the telescope's optical system. It is worth noting that some galaxies in the middle of the picture are distorted. This happens because the cluster of galaxies works as a big natural telescope. Imagine the universe as a massive trampoline, and planets, stars and galaxies as balls placed on it, their masses will distort the trampoline and, of course, the greater the mass, the greater the distortion. Light is thus bent by the cluster of galaxies and magnified. In this shot, the innermost galaxy's light goes back to 13.1 billions of years ago, and it would not have been possible to observe it without the help of this natural distortion.

Comparing the James Webb's debut shot (on the right) with a Hubble's image (on the left) of the same target, the technological progress and the new "eye"'s potentialities are palpable.

Not only does the JWST image has a much better resolution, but also the needed exposure times have decreased exponentially: whereas it had taken Hubble weeks to capture its best deep field, James Webb took only 12.5 hours.

You can admire a detail of the Carina Nebula, an interstellar agglomeration where the birth of stars was hidden for a long time by a curtain of gas and dust. It is at 7600 light-years from us, and it is one of the most luminous and massive nebulas in our sky. The region in the picture is the NGC 3324. Thanks to James Webb's ability to see beyond these layers of dust, we can finally admire the early stages of star formation, which individually last from 50,000 to 100,000 years only.

The essential won't thus be invisible to the JWST's eyes that, observing in the infrared, is able to see over the nebulas (interstellar clouds of dust and gas) allowing the scientific community to reach even more distant places in the space and, by consequence, in the time. The light that we will be able to observe in the future is indeed the one of the early stars and galaxies formation. It will be possible to go as far as the first stages after the Big Bang. Comparing our models to the gathered data, we can understand how our Solar System was born and observe it in greater detail. For example, we will be able to see more clearly the Uranus' rings, Saturn and Jupiter, the heat released by the volcanoes on Io (Jupiter's satellite) and by the comets that are approaching the Earth.

Among JWST's shots, we also find the Southern Ring Nebula, thanks to the work of two special tools: NIRcam (on the left), which is more focused on the star couple and their light, and MIRI (on the right), which prefers the observation of the luminous dust layers instead. We will be able to study the evolution of the star, how the surroundings are influenced by it and its death. The telescope itself discovered that the nebula is the product of not one only star, but two, with the dying one that orbits around the younger one, ejecting gas and dust, that will dissipate in the space over thousands of years.

Another one of the macro themes of research will be the evolution of the galaxies. There are several questions here, too. Why do the galaxies have a determined structure? Since when? Why do many galaxies have a black hole at their centre? Why do nebulas give birth to different types of stars? Why do the binary stars exist?

Moreover, it will be possible to measure with higher precision the speed of the universe expansion and observe the hotspots of forming planets.

The JWST has also photographed the Stephan's Quintet, a galaxy group, four of which interact gravitally, expanding and reducing each other. There are some details that were not observable before, such as the streams produced by the black holes at the centre of each galaxy.

The James Webb's goals are not over, though. Indeed, it will be able to analyse extra-solar planets' atmospheres, identifying eventual exoplanets, i.e. planets where humans could potentially live. Moreover, it can provide us with new data about the dark matter, the dark energy and the black holes' lifecycle, but its most astonishing ability is that it will provide answers to questions we have not asked yet. Many of the big revolutionary discoveries happened randomly or as an answer to a question completely different: the serendipity is fundamental in science.

Let's see the 4 tools thanks to which the JWST can observe so deeply. Unlike the telescope Hubble, which mainly works in the optic field, these tools all work in the infra field, with different specializations, also depending on the wavelength analysed.

The first one is NIRCam (Near InfraRed Camera), which focuses on the wavelengths between 0.6 and 0.5 micrometre. It also takes into consideration a bit of the visible light in the red-orange range. The electromagnetic spectrum is indeed compounded by several wavelengths, of which only a small portion matches the light that we can see. The colours the human eye sees go from red to purple - as you can notice when a beam of white light passes through a prism, while for greater wavelengths we find the infra-red.

The NIRSpec (Near InfraRed Spectrograph), instead, is a spectrograph. Each chemical element releases a trace based on its characteristics. A spectrograph like NIRSpec analyses the light composition, such as the one reflexed by planets, to obtain the chemical spectres of each pre-targeted area of space. Thanks to shutters, it can separates its visual field in sections, blocking the light coming from the section it wants to ignore and focusing all its attention on its goal.

Among the JWST's first results, there is indeed the WASP-96b atmosphere spectre, an extra-solar planet at 1150 light years from us. This is the most detailed spectre of an exoplanet ever done. Its analysis reveals the chemical signature of water, an indication of the presence of clouds, previously thought not to be present on the planet.

But NIRCam and NIRSpec do not work alone. MIRI (Mid InfraRed Instrument) is the main tool and the coldest one (its working temperature is -267 °C). It's made up of a photograph camera and a spectrograph that observes the mid infra range. It's thanks to MIRI that we can see through the nebulas.

The last one but not least it NIRISS (Near InfraRed Imager and Splitless Spectrograph), a spectrograph near to infra, accompanied by the Fine Guidance Sensors (FGS), which allow to orientate the telescope itself.

The gathered data are then translated to be understood by the human eye: each infra wavelength is assigned to a visible wavelength, allowing us to visualize the images already published last summer.

In conclusion, let's see the telescope's structure. A heat shield as big as almost a tennis field has the important duty to protect the "Fantastic 4" from Sun and Earth's heat, despite the distance of 1.5 million kilometres from it. The tools must work at very low temperatures in order to not fake the data with their heat or the one coming from our star or our planet.

The primary mirror, instead, has a total area of 27 square metres. Seen the telescope's dimensions, a key aspect of its design was to make everything as light as possible and foldable. This is why the mirror is composed by 18 hexagonal mirrors, each coupled with motors used to orientate them once the telescope was in space. The shield, on the other hand, was folded no less than 12 times and then stretched into orbit by a system that eliminated any wrinkles that would have compromised stability.

Will it then be possible to unmask the essential? The Hubble telescope has over passed by almost 15 years the duration of its mission and continues to impress us with always new discoveries. Who knows if the JWST will over pass our expectations, too. Only the time will give us this answer.

But you, reader, can tell me what you think about this topic and ask me anything you want at ctzn.eu@gmail.com or on Instagram writing at _ctzn.eu_.

Thank you for your attention,

Gaia Dimitri