The James Webb Space Telescope
What will the next-generation Webb telescope reveal? How is it different from Hubble? What will he allow us to see at the ends of the universe?
The story so far: The James Webb Space Telescope (JWST), launched into space by the Ariane 5 rocket from the European Space Agency’s spaceport in French Guiana, South America, on December 25 at 7:20 a.m. EST (5:50 p.m. HIST), is on his way to his destination. After a 29-day journey, the spacecraft will arrive at a point in space called “Lagrange point 2”, also known as L2. At a cost of 9.7 billion dollars, this joint project of the National Aeronautics and Space Administration (NASA), the ESA (European Space Agency) and the Canadian Space Agency is presented as the next-generation telescope . It is planned to unveil distant invisible parts of the universe and help unravel the mysteries of the cosmos.
- The James Webb Space Telescope (JWST), projected into space by the Ariane 5 rocket, will now be able to observe the far reaches of the universe without any atmospheric turbulence.
- After a 29-day journey, the spacecraft with the telescope will arrive at a point in space called “Lagrange point 2”, also known as L2. At this point, the gravitational forces of the Earth-Sun system and the orbital motion of the spacecraft would balance out. Therefore, the spacecraft positioned at L2 will orbit the Sun, accompanying the Earth in 365 days. It will also give the telescope the temperature required to detect weak signals from distant stellar objects.
- Since the diameter of JWST is larger than that of Hubble, it will collect more photons than Hubble’s 2.4 meter mirror. JWST will have about seven times more light collecting capacity than Hubble. Therefore, the JWST would observe fainter stellar objects that Hubble cannot detect.
What awaits the telescope in the next part of the journey?
The successful launch is just the start of an arduous journey of almost a month. The telescope was intricately folded like an origami toy before it was launched. Now in space, hundreds of moving parts will need to snap into place precisely as intended for the telescope to deploy. Over the next few weeks, step by step, various components must be deployed before the telescope reaches its final configuration. One misstep can reduce the entire telescope to space debris.
Accelerating to its destination, the JWST has now successfully deployed its solar panel, released its antenna, and completed its mid-term correction burn. Before day 7, the sun visor would be deployed. On day 10, nerves will be on edge as engineers hoist his secondary mirror to its position. The rest of the mirror segments would be deployed, step by step, by day 14. On day 29, JWST should fire its thrusters to enter its predestined orbit around L2. Once at the destination, the 18 segments of the telescope mirror should be perfectly aligned; it will take about 10 days. This will be followed by weeks of testing and calibration. The first telescope image is at least six months away.
Why are telescopes in space?
The thermal turbulence of the Earth’s atmosphere hinders telescopic observation of the universe. Stars twinkle, light from faint stellar objects is absorbed into the thick lower atmosphere, and part of the spectrum, like infrared rays from space, barely reaches the ground. By placing the telescopes on top of a high mountain, we avoid as much atmosphere as possible. Yet atmospheric turbulence hinders ultra-sharp images of objects in space.
Telescopes in space completely avoid atmospheric disturbances and give us a clear, crisp and deeper view of the far reaches of the universe. While the largest terrestrial telescopes have revealed galaxies more than 5 billion light years away, the Hubble Space Telescope has identified the most distant known galaxy 13.4 billion years in the past.
Why is JWST an infrared telescope?
The telescope mounted on the JWST is an infrared telescope. The invisible magic rays that change channels in our TV remote control are infrared. They are like visible light and radio waves, being part of the electromagnetic spectrum, but of different wavelengths. Why take an infrared telescope rather than a telescope capable of seeing the visible spectrum? The answer to this lies in the Big Bang.
After the Big Bang, galaxies, stars and planets evolved. Since the Big Bang, the universe has been constantly expanding. As the universe expands, space expands. As light travels far in space, the wavelength lengthens. The aged light becomes redder. Light from the first massive young stars and nascent galaxies was mostly visible and ultraviolet. However, passing through the vast expanses of expanding space, they transform into infrared rays before reaching Earth. An infrared telescope is able to observe the ancient and early universe, which is the main objective of the JWST.
What is the temperature at L2?
Primarily, the JWST is designed to detect weak signals from distant stellar objects in the infrared region of electromagnetic radiation. The IR telescope must be cooled to -220C or less. About 15 million kilometers from Earth, or four times the distance from the Moon, L2 is a freezing place. At this point in space, the second Lagrange point (L2), the gravitational forces of the Earth-Sun system, and the orbital motion of the spacecraft would balance out. Therefore, the spacecraft positioned at L2 will orbit the Sun, accompanying the Earth in 365 days.
As satellites orbit the Earth, they periodically switch from sunlight to Earth’s shadow and vice versa and are subject to thermal fluctuations. Placed at L2, JWST is permanently behind the Earth. When viewed from space, the Sun and the spacecraft will appear on opposite sides of the Earth.
Even at L2, the side of the telescope facing the sun will be at + 85C. However, on the opposite side, the temperature is -233 ° C. Using the tennis court-sized sunscreen would protect the telescope from the heat and glare of the sun.
Will JWST see better than Hubble?
Suppose we keep two bins in the open, one with a smaller radius and the other with a larger radius. During rain, the larger tub will collect much more rainwater than the smaller one during a given time. Likewise, the 6.5 meter diameter JWST telescope will collect more photons than Hubble’s 2.4 meter mirror. JWST will have about seven times more light collecting capacity than Hubble. Therefore, the JWST would observe fainter stellar objects that Hubble cannot detect. The further a thing is, the weaker it is. The JWST would see objects much further out in the universe with a larger collection area than Hubble. With its sharp eye, JWST can see the details of a twenty-five paise (penny) coin held at a distance of 40 kilometers.
The average time for light to reach Earth from the Moon is approximately 1.282 seconds. This means that the shining moon has 1.282 seconds. Because light takes nearly eight minutes for the Sun to reach Earth, the image of the Sun we see is about eight minutes old. The red giant Betelgeuse (Thiruvathirai Nakshatra) is 548 light years away. Therefore, the light of this star must have started its journey at the roundabout when Azhagan Perumal Jatavarman Parakrama Pandyan crowned himself king in 1473 AD. Take-home message: As we look far away, we look back.
How far can JWST look into the past?
Imagine the time of the Big Bang right now as a one-year calendar. In this cosmic calendar, the Big Bang occurred precisely at midnight on January 1. In this timeline, we are currently December 31st at midnight. JWST would allow us to see the universe as it has been since January 6. It was then that the first stars began to shine. Literally, the JWST would take us on a journey through time to an unimaginable ancient past.
A telescope can detect an object and show what it looks like. The spectroscope, a key instrument mounted on the telescope, can analyze light rays and tell us what is in them. From the spectral image, we can understand the elemental composition, the temperature of the stellar object and much more. Unlike Hubble, JWST carries the spectroscope, which should unravel the elemental makeup of early stars and galaxies.
TV Venkateswaran is Scientist F at Vigyan Prasar, Department of Science and Technology