Peering At Ancient Light, Webb Opens New Vistas
The James Webb space telescope survived the perilous journey of a million miles to its home in space and has settled there nicely.
And quickly enough, fruits are dropping to the floor and causing an unforgettable stir.
Our universe was born about 13 billion years ago in an explosive "big bang."
In the initial stages there was nothing more than a bunch of fundamental particles like electrons and quarks, which were floating around while the universe was expanding. There was no light, no matter, as we see it all around us today.
As things settled down, matter coalesced to form stars and planets. Stars clustered around to form galaxies. Forms of energy, like light, started taking shape. An infant universe was in its diapers.
As the universe continues to expand, what we see around us are recent happenings. So the further we look out, the older the structures we see. Even with light travelling at seemingly infinite speeds, it takes millions and billions of years to travel across the, again, seemingly infinite universe.
In an expanding universe, the light reaching us is stretched out, much like the pitch of an ambulance's siren, which changes as it approaches us and recedes from us. In case of light, the stretching results in conversion to infrared light, which humans cannot see, but the complex instruments we build can.
These instruments, built to watch the very distant horizons of the universe, are telescopes. Humankind has built some of the most sophisticated telescopes in remote areas like Hawaii and Chile.
Ground-based telescopes have a layer of the Earth’s atmosphere in between, which distorts the incoming light to an extent. To overcome this limitation, space telescopes were built to get unfettered images. The Hubble telescope has been the vanguard of such a technology and gave us excellent images of the early universe.
Recently, we took a step further to launch the next generation of space telescope, called the James Webb space telescope, dubbed as "the ultimate space telescope."
Decades in the making with several massive cost overruns, the telescope was launched on Christmas day of 2021. The Webb telescope can see the universe as early as 200 million years old, which is an exceptionally tiny sliver compared to the age of the universe.
The eyes of the telescope are its mirror. The bigger the mirror, the better the sight. But bigger mirrors are nearly impossible to cast as a single piece. Even if we can cast such a mirror with great difficulty, transporting such a single piece into space aboard a rocket would be impossible with the current launch facilities.
Webb's mirror was designed as a collection of 18 hexagonal segments, each made of beryllium and coated with a thin layer of gold. The picture below shows the mirror compared to Hubble’s mirror and the size of a human standing beside them.
In this way, the mirror could be folded and sent into space.
Relocating to a New Home
Because Webb sees exclusively in the infrared region, there cannot be any sources of heat nearby, including its own heat. This is because heat itself is a form of infrared radiation. The nearby sources also include the Sun, Moon, and Earth.
The telescope, therefore, had to be cooled to very, very low temperatures, close to absolute zero. Secondly, the positioning of the telescope was critical. Anywhere closer to the Earth or Moon would make the heat intolerable. There are considerations of gravity from the Sun, Moon, and Earth and the fuel required to maintain Webb's position in space.
After due considerations, the space telescope was designed to be parked in a point called L2 or Lagrangian point 2.
As shown in the picture below, L2 lies on the Sun-Earth axis as far as possible from the Sun, Earth, and Moon. It's about a million miles away from the Earth. Yet, it is gravitationally suitable where the forces from all the three bodies balance and the telescope can hang in there with expending a minimal amount of fuel.
The five Lagrangian points shown in the picture resulted from a solution to the three-body problem solved by the French mathematician Joseph Lagrange. The telescope orbits the L2 point in a plane perpendicular to the Sun-Earth axis. With minimal fuel consumption, its fuel reserve is expected to last a decade.
Since the Sun, Earth, and Moon are on one side of the telescope while it is looking in the other direction, a five-layered heat shield protects the telescope. While on one side of the tennis court-sized shield, the temperatures are searing hot, on the other side, the telescope is a freezer.
Beryllium was chosen as the material for the mirror because its expansion and contraction due to temperature differences are minimal. It is lightweight, but very stiff to encounter the harshness of space. It is coated with a very thin film of gold to get maximum reflectivity. It is massive, yet it is about a tenth as heavy as Hubble’s mirror.
The picture below shows the telescope with the heat shield and mirror unfolded.
The James Webb space telescope survived the perilous journey of a million miles to the L2 point. The unfolding of the heat shield and mirror proceeded flawlessly. The alignment of the mirrors had to be done in a slow and precise manner to get the perfect picture. The attached motors could move each mirror by a tiny fraction of an amount. The motors had to move slowly so as not to generate heat. This is why it took several months to complete the alignment.
With each new generation of electronics, the detectors become more sophisticated and sensitive, very much like our cell phones. The basic instrumentation is a camera and a spectrograph. The camera captures the image, while the spectrograph splits the incoming radiation into different frequencies (colours for visible radiation).
Fruits of the Webb Tree
After all these laudable efforts by an army of scientists and engineers, we have the first set of pictures from the Webb telescope released recently. They are spectacular. More like Van Gogh paintings. My favourite is the one titled “SMACS 0723 galaxy cluster.”
Obviously, such complex images are assembled from thousands of individual pictures, and colours are assigned based on the frequencies of the signals received. The blank patches of the sky are not really blank. Intense observations can produce such a colourful image.
Other than viewing the original glare from the infancy of the universe, Webb is all set to help detect exoplanets — the planets outside of our solar system. Webb has a coronagraph, an instrument which blocks out the brilliant glare of the central star and helps the infrared detectors gather information from the orbiting planets.
Located at a vast distance where no human has ever gone, the telescope will have to be abandoned if it cannot be fixed. There cannot be any servicing missions of any sort. So far, things are looking good except for a few meteorite strikes that did cause some minor damage.
Let's hope for the best for Webb. Such scientific observations triggered by engineering marvels inspire us. Not long ago, Hubble was the ultimate space telescope. Now it is Webb. What would the future space telescope look like?
Given how Webb's been able to see unfathomably far back in time, perhaps, the next-generation telescope may attempt to look back when the universe was still in its mother’s womb.
Until then, shine on, you crazy Webb.
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