Techies create the specs of the James Webb telescope, pictured in 2017.
Photo: Laura Betz / AP / SCANPIX
Rūdolfs Treilis, a physicist, holds a PhD from the University of Durham (England), “Latvijas Avīze”, JSC “Latvijas Mediji”.
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The most powerful telescope of all time, named after former NASA leader James Webb, was launched from the Cruz Cosmotrome in French Guiana on Saturday, December 25th. The telescope, which is supposed to study the oldest galaxies in the universe, is expected to reach a target 1.5 million kilometers away in 1.5 weeks. We already reported this important event for science on December 21 in “Latvijas Avīze”. In this issue we publish the article by physicist Rudolph Trailis.
About 14 billion years ago, the entire visible universe was in a matchbox. It contained a soup of exotic particles that spread evenly in all directions of the room and was heated to a temperature that appeared to be much cooler compared to our sun. After a second, only the most familiar particles remained – protons, electrons and neutrons – but the universe was still very hot.
The first heavy elements, helium and lithium, were formed in this primary smithy, but three minutes later the universe cooled enough to make thermodynamic nuclear reactions impossible. It sank into the deep darkness filled with glowing plasma, which, paradoxically, was opaque to the light it expressed.
The situation remained unchanged for the next 400,000 years, until the universe finally cooled enough to allow plasma to condense. Suddenly, the space was filled with large clouds of hydrogen and helium, which were exposed to the original glow that remained from the moment it was created. Photons of this light began a long and tedious journey through the now-empty universe, 13.8 billion years later some of them struck a small satellite orbiting a distant galaxy around the indescribable planet.
It is amazing how the people of this planet can get information about the history of the universe by looking at a part of the endless mystery. They observed that the early universe was almost identical and that their gas was in excellent thermal equilibrium. However, there were small contractions of the material and slight fluctuations in temperature around the mean value.
Over time, these compounds grew and contained more and more surrounding gas; They warmed up and began to glow around, even in the background. 180 million years later, the first stars were born from these primitive eruptions. They were brighter and larger than the stars we see today, and although their lives were very short, the universe ended up with huge explosions filled with very heavy elements. Due to the force of gravity, these elements began to stick together over time, and billions of years later the already unspeakable planet and its people formed. Although this planet does not really stand out from the surrounding background, its people are special and curious; They now plan to open a brand new telescope in the dark depths of the sky and observe their own creation.
The technology is amazing
The James Webb Telescope is an absolute marvel of engineering and technology. It was developed jointly by NASA (from the US), ESA (from Europe) and CSA (from Canada) and cost approximately $ 10 billion.
This telescope does not use the visible part of the light spectrum, but slightly longer wavelengths called infrared radiation. This choice is triggered by the goals set for this telescope – to look at the history of the ancient universe more than any telescope has ever been able to do. Although the primordial stars I described above have been exposed to the visible and ultraviolet regions of the spectrum during their lifetime, due to the expansion of the universe, this light now extends into the infrared radiation detected by the James Webb telescope.
However, the choice of this spectrum significantly complicates its location and construction because any hot body (like the same telescope) emits infrared radiation, which completely suppresses any optical signal from the depths of the universe. This problem is certainly not theoretical: by its optical structure the objects we want to see are placed on the surface of the moon and are 10 times brighter than a tiny reading lamp seen from Earth.
And the five Lagrange points in the Earth-Sun system. L2 is beyond lunar orbit and cannot be reached by humans.
Photo is not Wikipedia
This means the telescope must be far away from the infrared source (Earth and Moon) and cool to an incredibly low temperature (below 50 K, 223 degrees Celsius). This is achieved by placing the Lagrange points at one of the L2 (see picture) and shielding them from the sun’s hot radiation with a large foil shield. Five special (lagrange) points can be identified in the orbit of two bodies connected by gravity. A small body placed at these points will maintain its orientation relative to the two larger bodies, and requires very little fuel for its steady operation.
L2, the farthest point from the Sun and closest to Earth, was chosen to reach the web telescope in a few weeks (one and a half million kilometers from Earth) with the rocket’s telescope.
However, when the telescope is placed in this place, it will be constantly attacked by the light coming from the sun, which heats up to a high temperature and it becomes inoperable. To solve this problem, the earth and sun-shielded aluminum shield does not absorb or reflect sunlight by cooling the telescope (its core requires active cooling using a thermostatic device specifically designed for this project).
Gold plated glass
The optics of the telescope are also remarkable. Its core is gold-plated glass more than six meters in diameter and polished to a precision comparable to just 50 atoms (for example, a hair is about 20,000 atoms wide). Choosing gold to cover glass may seem strange because it is not really the best reflective material in the optical spectrum, but the condition of the infrared light is different and – in combination with the relatively good resistance of gold to low temperatures – this is the best choice.
Selecting a larger glass diameter improves its performance in two ways: first, it can collect more light and feel dim objects, and secondly, the wavelength of light controls the maximum resolution, and allows larger diameters to distinguish smaller angles.
The glass diameter of the Hubble telescope (which can be considered a web telescope) is only two meters in diameter, so we can expect significant improvements in optical quality (the resolution is similar to that of the Hubble telescope because the light wavelength is higher than that of the web telescope).
However, the history of the Hubble Space Telescope can provide valuable insights and identify potential dangers to the Internet telescope. When the Hubble telescope was first placed in orbit, it had a small flaw in the glass – polished to an accuracy of up to fifty times the width of its hair. However, the defect was large enough to blur all images sent from the telescope. For Hubble’s first maintenance, adaptive optics were added to fix the defect. Internet telescopes do not have this possibility, because they are within human reach of the earth, so do not make mistakes. To avoid the possibility of such a catastrophe, a mirror is added to the telescopic mirrors of the web, which allows them to control the radius of curvature and the resulting focal length very precisely.
Exciting days
The Internet telescope was launched into orbit on December 25. It was an exciting, exciting day for the entire community of astrophysicists and astronomers, followed by 30 days full of similar tensions, during which the telescope reached L2. There are several important points during the start-up, from the survival of the mirrors to the automatic loading of the orbit and the proper opening of the sun visor.
Many physicists and engineers have sacrificed most of their lives so far, and now it has finally arrived! If the launching process is successful and the telescope operates, we can explore the ancient history of the universe. Can see the first galaxies and stars; To better understand the role of supermassive black holes in the structure of the universe and whether they are needed as germs in the formation of galaxies; Look at the many new exoplanets – perhaps like Earth – and distinguish their atmospheric spectra, their chemical distribution and whether life can exist on the planet’s surface. As a physicist my soul screams that this is just superstition, but on December 25 I grabbed my thumb!
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