July 17, 2022

Webb Telescope Opens a New Window in the Sky

Prabir Purkayastha

THE new Webb telescope has already shown that NASA's $10-billion investment and 26 years finally is delivering its promise: pictures of the cosmos at depth, in detail and quality far beyond what we currently have. The first set of images has captivated the general public, while the astrophysicists are drooling at the details and the spectra of the distant objects, telling us what they actually are. For those in astrophysics who started their career even before the Hubble telescope, this is witnessing two revolutions in astrophysics – Hubble and Webb – all in one generation.

The set of pictures are astounding in their details and, therefore, the promise they have for the future. One picture is a galaxy cluster SMACS 0723, which has thousands of galaxies – including some of the faintest objects ever observed. NASA says, "Webb's image is approximately the size of a grain of sand held at arm's length, a tiny sliver of the vast universe. The combined mass of this galaxy cluster acts as a gravitational lens, magnifying more distant galaxies, including some seen when the universe was less than a billion years old."

Since light takes a long time to reach us, not only are we looking at distant galaxies but also at the light that left these stars/galaxies 13.1 billion years ago. The Big Bang is estimated to be 13.8 billion years back. So we are not only peering at objects a long distance away but also a long time back. The Webb telescope is, therefore, like a time machine: it also allows us to look back in time. If we go further, we may reach a period "shortly" after the big bang. How much farther back? Another 300-400 million years? More? That is the question that Webb's researchers will answer in the future. All we know today is that we will learn far more about our cosmos with Webb and other such instruments.

The longer the distance from the object we observe, the more the object's light shifts towards the spectrum's red side. This red shift is also known as the Hubble effect. So the Webb telescope operates more in the infrared spectrum than the earlier Hubble telescope, which operated more in the visible spectrum. And yes, visible light is a small part of the total electromagnetic spectrum; that is why we need from radio telescopes to the Webb telescope, each with its version of the story of the cosmos.

The Webb telescope also has spectrometric instruments that tell us the composition of the elements that constitute the star. We can see the spectrum of hydrogen, oxygen and other components. That brings us to the next image of an exoplanet circling a nearby star, only 1,000 light years away. An exoplanet is a planet orbiting another star, not our sun. The question is, how many of such planets have water and, therefore, the possibility of life?

This exoplanet, WASP-96 b, is a gas giant and one of more than 5,000 confirmed exoplanets in the Milky Way. It has a temperature greater than 600 C and is significantly hotter than what can sustain life. It orbits extremely close to its Sun-like star and circles it once every 3½ days. As the planet passes in front of its star, the light from the star passes through the planet's atmosphere. By examining this light, we can see what is called the absorption spectra, or what the planet's atmosphere has absorbed and, therefore, the composition of the planet's atmosphere. While this planet cannot support life, in the future, Webb can help us analyse many of the exoplanets in our galaxy and the potential of extra-terrestrial life.

There are other images that Webb has delivered. One is a set of 5 galaxies close to each other in what NASA calls their cosmic dance, "Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image. Sweeping tails of gas, dust and stars are being pulled from several of the galaxies due to their gravitational interactions. Most dramatically, Webb captures huge shock waves as one of the galaxies, NGC 7318B, smashes through the cluster.” There is a picture of a star birth in the Carina Nebula, and an image of the Southern Ring planetary nebula, which shows the final "performance" of a dying star. Hubble also has a picture of this nebula, and comparing the two shows how much more details Webb gives us.

While the scientists are wowed by the details of the cosmos that Webb is delivering and can deliver in the future, the engineering feat of building a telescope in space is also quite astounding. The Webb telescope had to be carried in a dismantled state to space 1.5 million kilometres away and then assembled there remotely. It was placed in a position where the sun's gravitational pull is balanced by the earth's pull, which the astrophysicists call a Lagrange point.  One mistake – the engineering team had identified more than 300 such possible mistakes – would have meant curtains for the mission: the $10-billion project would have been over before it could even start its work.

Webb has a 6.5-metre mirror that gives it six times the light-gathering surface of Hubble, increasing what it can see significantly. Unlike the Hubble, which uses visible light, Webb's telescope is far more sensitive to heat, as it uses the infrared part of the spectrum; therefore, its deployment so far from the earth. The Webb also has a sunshade that keeps the mirror at -220 Deg C, which is essential for its functioning. Otherwise, its higher temperature would drown out the infrared radiation from distant stars.

While all major advances in science are not on based on huge costs, increasingly major advances in science will require industrial-scale efforts with large teams and budgets. Not that there will be no more the individual brilliance of an Einstein or a Bose, but major advances in the experimental part of physics will require large budgets and teams. While people remember Higgs, they "forget" the Boson part of Higgs Boson, named after Satyen Bose for his contributions.

With its $10-billion cost, the Webb telescope is currently the most expensive instrument ever built, beating the Hadron Collider with its $4 billion costs to the second place. Yes, it is expensive to advance knowledge today. But compared to an aircraft carrier, this is still less: Gerald Ford, the latest US aircraft carrier, cost $13 billion. That is the travesty of human civilisation. We are willing to spend far more to destroy than to create, to satisfy the imperial needs of the rulers.

Undoubtedly, Webb's telescope will open new vistas for astrophysicists. Apart from learning much more about our cosmos, it may help us find dark matter, which has proved elusive till now. Though a special telescope is being launched for this purpose, Webb will play an important complementary role in this process. The second is, it could help settle one of the biggest controversies in modern astronomy: what is the true expansion rate of the universe? This number also called the Hubble's Constant, is the rate of cosmic expansion per every megaparsec (roughly 3.26 million light-years) of space. Depending on the method used, the measurements of this number cluster around two values, 67 and 73. Given the high-precision agreement that exists for other cosmological measurements, these numbers are too far apart. While the astrophysicists call this the "Hubble tension", it is far better described as the Hubble headache.

One last comment about Webb. A number of scientists are bitter that this wonderful new observatory is named after Webb, a career bureaucrat who led NASA at a time when the US Federal government and NASA actively followed a policy of homophobia and sacking employees on this count. These scientists mounted a campaign to rename the Webb telescope as the Harriet Tubman Space Telescope, in the memory of Harriet Tubman, who ran the underground railroad for those escaping slavery in the US south. I end with the quote from Chanda Prescod-Weinstein, Sarah Tuttle, Lucianne Walkowicz, and Brian Nord, the scientists who led this campaign, "The time for lionising leaders who acquiesced in a history of harm is over. We should name telescopes out of love for those who came before us and led the way to freedom – and out of love for those who are coming up after." Not to celebrate those who helped deny us of our freedoms.