09/07/2019
I am very pleased to report that the $10 billion James Webb Space Telescope, Hubble's long-awaited successor, has finally, been, fully assembled after more than 20 years of dedicated effort. Engineers recently connected the two halves together (spacecraft + telescope) mechanically through the use of a crane. Set to launch in March 2021 and to orbit at 1.5 million kilometres away from Earth, the James Webb Space Telescope will peer back in space and time to give us a look into the young exploding stars that ignited in the early universe. The promising instrument will also look for planet-forming disks of dust in our galaxy and search for potential life abodes beyond the solar system. As it revolutionizes our understanding of the universe, this next generation observatory is set to become the next giant leap in observational astronomy.
The James Webb Telescope will have a 6.4 metre-wide mirror, about 7 times larger than Hubble’s, and thus an ability to gather light 70 times more than Hubble. The mirror structure will be formed by 18 beryllium segments, 20 kilograms each. The telescope will also possess a sunshield of astronomical size — almost the size of a tennis court. A parasol sunshield, it will be a five layered-structure, with a vacuum separating each layer. That is because the sunshield will serve to separate the telescope into a warm side and a cold side, as the telescope is pointed to the sun. The cold side is needed in order to seclude the sensitive filters, detectors, and mirrors from the sun’s heat. The sunshield will, indeed, only allow through less than one-millionth of the sun’s heat! Having a vacuum between each layer ensures that each layer will radiate away any heat so that virtually no heat gets to the cold side.
There will also be a smaller mirror opposing the larger one. Light will bounce off the larger mirror into the opposing one and then on onto the cameras and instruments. The mirrors are infrared mirrors and they will need to be kept at such low cryogenic temperatures of about -233 Celsius degrees so that they are not a source of infrared radiation themselves. Otherwise, that would interfere with photons being looked for. The telescope will also have a near-infrared camera with a larger field of view than Hubble’s. The camera will have a corona-graph to make faint objects visible and will serve to detect light from the universe’s earliest stars and galaxies.
The telescope will be positioned opposite the sun at the second Lagrangian point (L2) which is four times further away from Earth than the moon is. At this point, the telescope, the Earth, and the Sun would be lying in the same position in a straight line, since the gravitational forces and orbital motions of the bodies balance each other, establishing a stable position between Earth and the James Webb telescope and allowing for ease of communication.
One of the reasons why this telescope is pitted to be very promising and revolutionary is that, unlike the Hubble Space Telescope, the James Webb Telescope is an infrared telescope. Since the beginning of the big bang, the universe has been expanding. As the universe expands, the galaxies move apart from each other. Light travelling from those galaxies is therefore stretched in the process. In other words, light is red-shifted towards the red end of the electromagnetic spectrum. Thus, light emitted from the far-away first galaxies (that started travelling billions of years ago) would be shifted to the infrared end of the spectrum.
Infrared astronomy is also quite important when peering back through clouds of dust in order to observe stars and planets lying behind them. Clouds of dust can block objects in space from view because they absorb visible light. Infrared light from such objects however would be able to “penetrate” such occluding clouds of dust. A telescope optimized for infrared light would therefore allow us extend our vision into a hidden past world - an ability would allow us to trace the earliest stages of stellar evolution!
If Hubble’s history is any indication, we are yet to imagine what the most powerful telescope ever built will unravel!
