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James Webb Telescope: light on dark matter


Humanity’s fascination with the sky is as old as humanity itself. The sight of countless stars and the faint band of light stretching from horizon to horizon must have been the cause of wonder and awe for the first homo-sapien as he plodded along the along the plains of East Africa. From hunter-gatherer to modern times, each culture has developed its own cosmology — the system of beliefs or theories that explain the origin and structure of the universe.

To study the heavens, a variety of instruments have been used throughout history. From sundials and astrolabes to telescopes and now gravitational wave detectors, we have tried to observe, map, study and measure the universe. These observations have, in turn, led to the formulation of our theories of the universe. Thus, it was Kepler’s observations of the planets that gave Newton the impetus to formulate his law of gravitation which still forms the basis of celestial mechanics. In the early 20th century, Hubble’s observation of receding galaxies led to the model of the expanding universe.

The quest to probe the universe received a major boost with the commissioning of the James Webb Space Telescope. Costing around $10 billion, the telescope took more than three decades from planning to commissioning and is truly a symbol of humanity’s intellectual and creative potential.

Launched in 2021, it reached its final orbit at a distance of around 1.5 million km from Earth in early 2022 and it took engineers and scientists another six months to prepare the instruments before they could be used. The observatory has four main components – the Integrated Science Instrument Module (ISIM) which houses four instruments to analyze the light captured by the optical telescope element featuring a 21-foot-diameter gold-plated beryllium primary mirror composed 18 hexagonal mirrors and a secondary mirror to guide the light collected by the primary mirror to the instruments. There is also a huge collapsible sunshade to block radiation from the Sun, Earth and Moon since the instruments have to operate at -220 degrees Celsius. Finally, there is the space bus with all the equipment for the operation of the observatory.

And then finally it happened: in July, he released his first images and they were truly breathtaking. The images of galaxies that could date from almost 13 billion years ago, the cosmic cliffs of the Carina Nebula, the Cartwheel Galaxy, Stephan’s Quintet – each one of them was spectacular even if the colors were artificial since the images were infrared images and not visible light. It also provided an analysis of the atmosphere of a gas giant planet orbiting a star about a thousand light-years away. The analysis indicated the presence of water in the atmosphere.

Developments in telescope technology (in all regions of the electromagnetic spectrum, not just the visible region) over the past century have allowed us to know with reasonable certainty much about our universe. We know that in the “beginning” of time, all energy was concentrated in a primordial fireball of extremely high temperature and density. Then, with a massive explosion, dramatically called the Big Bang about 14 billion years ago, the universe began and has been expanding ever since. At some point, a few hundred million years later, the first stars began to form.

Although the broad outlines of the universe are fairly well established, the details are still lacking. This is especially true of the earliest times in the history of the universe. This is where the Webb Telescope offers a unique opportunity.

Our window to the universe is electromagnetic radiation. These waves, which span a spectrum of wavelengths from very long radio waves through visible light to ultra-short gamma rays, propagate at the speed of light. This means that in cosmology, given the enormous distances involved, if one looks at the waves emitted by a very distant object, one is actually observing the object as it was in the distant past – to look into the distance means to look in the past . The expansion of the universe also stretches the waves and so visible light could be stretched into the longer infrared part of the spectrum. Infrared radiation has the advantage of passing through dust clouds more easily than visible light.

The Webb has four instruments to observe and analyze infrared waves. This makes it uniquely suitable for observing light emitted from the earliest epochs of the universe. This will give us insight into how the first stars and galaxies formed from the primitive soup of matter and radiation. Because it can peer so far into the past, it will also allow us to compare the earliest galaxies (those farthest away) to those we observe today in our own cosmic neighborhood. And because it operates in infrared, it can see through dust clouds that obscure regions where stars and planets form.

The Webb doesn’t just produce pretty images. It also produces an enormous amount of spectroscopic data that reveals, among other things, the chemical composition of the region producing the radiation. Studying the chemical composition of exo-planets – the planets orbiting other stars – would determine whether life as we know it is possible on these extraterrestrial worlds.

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In 1543, Polish astronomer Nicolaus Copernicus published a book that revolutionized our understanding of the cosmos. We have been moved from the center of the universe to another planet revolving around the Sun. Centuries of sightings since have made us even more insignificant. Over the past few decades, it has been shown that the kind of matter our world is made of – the matter in our iPhones, our earth, and even us, is only 3-4% of the matter and energy global in the universe. The rest is a combination of a mysterious type of matter called dark matter and an even more mysterious unknown substance called dark energy. Not only are we not at the center of the universe, we are not even made up of the kind of matter that the universe is mostly made up of. Any vestige of our species’ anthropogenic arrogance has finally been demolished by cosmology. The universe is vast and most of it is unknown. We hope that the Webb, over his lifetime, will provide us with a powerful window to help solve some of the many mysteries of the cosmos and make it a little more understandable.

The author is a professor of physics and astrophysics at the University of Delhi