On December 25 of last year the space telescope james webb was launched into space from French Guiana aboard an Ariane 5 rocket, reaching its final destination on January 24. Built and operated by European Space Agencies (THIS), American (POT) and Canadian (CSA), the James Webb is the new member of the saga of space telescopes that follows in the footsteps of the Hubble and the spitzer. With a mirror made up of 18 segments and a diameter of 6.5 meters, the James Webb will cover the range of the light spectrum from the visible to the mid-infrared with four instruments on board, both in imaging and spectroscopy. Among the scientific objectives of the mission, the exploration of the “cosmic dawn” stands out, a poetic name that evokes the moment in which the universe was illuminated with the light of the stars that were born in the first proto-galaxies.
Throughout the universe we observe very diffuse clouds of matter that barely contain one atom per cubic meter, forming the so-called intergalactic medium. Submerged in this gaseous ocean we find the galaxies, huge conglomerates of matter illuminated by the stars they contain inside. Galaxies are the largest objects that exist in the universe, except for the structures that they draw when they group together, an authentic “cosmic web” made up of large clusters, filaments and voids that is known by the name of the large-scale structure of the universe”. The detailed study of it is of enormous importance to prove the validity of the cosmological models.
The galaxies they are made up of billions of stars accompanied by their respective families of planets, satellites, asteroids and comets, together with clouds containing gas and small agglomerates of particles known as dust. They are also surrounded by a huge halo of “dark matter”, so called because we cannot see it directly as it is made up of particles that do not interact with light. We know, however, of its existence, albeit indirectly, through the gravitational effect that it exerts on visible matter.
There is a wide range of types of galaxies. Elliptical, rugby ball-shaped and reddish in color. Spirals like the Milky Way, very visually spectacular with its reddish central bulb and the thin blue disc where its characteristic arms are located. Irregular, with a poorly defined shape, somewhat smaller and blue in color. Next to them we find the dwarf galaxies, much smaller and more abundant, displaying a wide variety of shapes and colors. While normal galaxies can contain hundreds of billions of stars, dwarf galaxies barely contain a few billion at most. The color of galaxies is a very interesting property since tells us if the galaxy is currently forming stars. We know that the more massive a star is, the hotter its surface is, which makes its color bluer, and also that it lives less time as it is very efficient at burning the fuel it has inside. As an example, a red star with 25% of the solar mass can live a billion years, while a blue one that is about 25 times more massive than the Sun, “only” will live about 10 million years before explode as a supernova. Therefore, the blue color of a galaxy will be indicating that there has been star formation in a very recent time since it still has many massive stars with short lives.
only in the observable universeit is estimated that there would be around a trillion galaxies, a fact that the telescope James Webb will help pin down. How did this multitude of galaxies form in the early universe? What factors have determined the variety of sizes, shapes, and colors that we see today? How is its evolution articulated with the formation of large structures?
According to him cosmological principlethe universe is homogeneous and isotropic, something that has been widely corroborated by observations. For astronomers, this fact provides an enormous advantage, since it means that what we study in any area of the sky will be representative of what is happening throughout the universe. It is evident that this uniformity is only true when we observe on a very large scale; at smaller spatial scales, when we increase the resolution, there are indeed inhomogeneities. In fact, otherwise there would be no place for the existence of any type of structure, that is, there would be no galaxies, no stars, no planets, no living beings like us… The universe would be an extraordinarily boring place!
To find the origin of these irregularities we have to go back to the first moments of life of the universe, to the so-called “inflationary period”. During a very brief moment of time, very close to “instant zero”, an enormous amount of energy was released that caused a very rapid, “inflationary” expansion of the universe. In less than a trillionth of a second, the universe went from the size of a proton to the size of a tennis ball, greatly amplifying the tiny existing perturbations produced by the quantum fluctuations. After the inflationary period, the irregularities continued to grow at a much slower rate, due to the combined effect of expansion and gravity, until they became the shoots from which the structures we observe in the present universe will grow.
The process of galaxy formation began more than 13 billion years ago, when the universe was only a few hundred years old and much smaller, denser and hotter than it is today. Due to the gravitational attraction, the areas with the highest density had been growing by the accretion of surrounding matter, until they reached the necessary conditions to start the formation of stars. The dynamics of the process star formation it is very complex; the large gas clouds break up into smaller clouds, which are the ones from which the stars are formed, which tend to be born in large groups. The formation of a star is produced by the collapse of one of these smaller clouds, due to its self-gravity. The density and temperature increase until the necessary conditions are reached inside the cloud for the fusion of hydrogen into helium to begin, at which point we can say that the star “has seen the light”, and never better said.
With the birth of that first generation of stars, known as population III, the first proto-galaxies made an appearance in the universe. The population III Stellar was formed from what is known as “primordial material”. At that time there were only hydrogen, helium, lithium, boron and beryllium atoms formed from elementary particles in a process known as primordial nucleosynthesis, when the universe was about 3 minutes old. According to theoretical models, it is believed that Population III stars must have been huge, several hundred times more massive than the Sun. With a lifetime of only a couple of million years, they exploded as spectacular supernovae, expelling huge amounts of carbon dioxide into the surrounding gas. heavy chemical materials that had been processed inside. From this gas would be born the stars of population II, which will continue the process of enrichment of the environment, and later those of population I like our Sun, very rich in heavy elements.
Supernova explosions release huge amounts of energy that “sweep up” the surrounding material, overlapping each other to cause the formation of huge winds that flow out of galaxies. To this phenomenon we must add the frequent processes of fusion of some proto-galaxies with others, at a time when the universe was much smaller than the current one. In fact, current theories indicate that galaxies formed in a bottom-up process (“bottom-up”), through a complex combination of gas accretion, massive star formation, and galactic mergers. The global process is so extraordinarily complex that to understand it it is necessary to resort to numerical simulations that incorporate the entire battery of physical phenomena to be taken into account: from the cosmological model that includes the content of dark matter – an essential component to reproduce the formation of structures – to models that simulate the formation and evolution of stars without forgetting all the complex (magneto)hydrodynamic processes of the gas. The result is a “simulated” universe with “simulated” galaxies”, which allows us to delve into all the details and physical mechanisms that come into play. It goes without saying that, before drawing any conclusions, these simulations must be contrasted with observations of the real universe to validate the different hypotheses they incorporate.
This is precisely what the new James Webb telescope offers us: the possibility of directly observe the epoch in which galaxies formed to collect an enormous amount of data with which to contrast the theoretical models. At this point we must remember that the fact that the speed of light is finite gives us a true time machine: the further we look, the longer it has taken for light to reach us. As an example, the Sun we see right now is the Sun it was 8 minutes and 20 seconds ago, just as long as its light has taken to travel to Earth. With telescopes of the power of the James Webb we will be able to observe very far away, so much so that the light will have taken more than 13,000 million years to reach us, providing us with a direct image of what happened at that time. There is a second detail, no less important, that we must also take into account. The expansion of the universe causes light to “stretch” on its journey, shifting its wavelength to longer wavelengths (the famous red shift). This makes very distant objects very dim in visible light, as the light has shifted into the infrared on its journey. For this reason, infrared telescopes like the James Webb they are ideal for studying the most distant galaxies in the universe. As indicated by the ESA, if the Hubble Space Telescope has been able to reach the infancy of galaxies, the James Webb will show us what they were like as babies. An authentic journey through time that will take us to the cosmic dawn.
In these times in which utilitarianism subordinated to the economic system predominates in society, one might wonder what is the use of knowing the details of the cosmic dawn. The answer is as simple as it is pertinent: for the pleasure of meeting you. We know that in order to successfully face the environmental emergency, we must make a change in our way of life, which begins by unmasking the myth that identifies wealth with money. This is something that we can only achieve if we learn to revalue human relationships, art in all its various manifestations, the unfathomable beauty of nature and, of course, the pleasure of knowledge. per se. After all, the success of humans as a species is due to the fact that, deep down, we are and will continue to be explorers of the beautiful and unique complexity of our universe.
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