Peering Back into the Cosmos

As our sense-extending technologies continually project the far elusive reaches of the universe into the confines of our cognition, we find ourselves constantly defining the word observable. NASA’s long-awaited Hubble successor, the James Webb Telescope, is finally taking shape as it promises to give us an unprecedented glimpse into the history of our early universe. Just today at the NASA’s Goddard Space Flight Centre, the James Webb Telescope got the first of its 18 hexagonal flight mirrors installed. Set to launch in 2018 and to orbit at 1.5 million kilometres away from Earth, it will peer back in space and time to give us a look into the young exploding stars that ignited in the early universe. The magnificent 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 will certainly become the next giant leap in observational astronomy!

The Successor to the Space Throne 

Succeeding Hubble to become the next cosmic watcher, the James Webb Telescope will have a 6.4 metre-wide mirror, about 7 times larger than Hubble’s and has the ability to gather light 70 times more. Eighteen beryllium segments, 20 kg each, will come together to form this wondrous mirror structure.

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Cryogenic testing on mirror segments at NASA’s Marshall Space Flight Centre. Credit: NASA
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First mirrors being tested at NASA’s Goddard Space Flight Centre. Credit: NASA

The telescope will also possess a sunshield of astronomical size — almost the size of a tennis court. This parasol sunshield 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. In fact, the sunshield will allow through less than one-millionth of the sun’s heat! Having a vacuum between each layer thus allows each layer to radiate the heat away so that virtually no heat gets to the side.

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Sunshield serves to protect instruments from solar heat. Credit: NASA

There is also 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 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 also has a near-infrared camera with a larger field of view than Hubble’s. The camera has a corona-graph to make faint objects visible and will serve to detect light from the universe’s earliest stars and galaxies.

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The James Webb Telescope. Credit: NASA
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JWST’s primary mirror vs. Hubble’s primary mirror. Credit: NASA

The James Webb 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 (1.5 km away). This is so as to protect it from the sun’s radiation. At this point, the telescope, the Earth, and the Sun would lie in the same position in a straight line. That is because the gravitational forces and orbital motions of the bodies balance each other. Accordingly, a stable position between Earth and the James Webb telescope will be attained. This allows for ease of communication.

The Infrared Universe 

The James Webb Telescope is an infrared telescope, allowing it to peer back into the very distant stars and galaxies that were first formed in the early universe – much more than Hubble can see with visible light. But why use 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 would be shifted to the infrared end of the spectrum. This is light that started travelling billions of years ago.

 

The Pillars of Creation — visible and infrared comparison
Unlike JWST which is optimised for infrared light, Hubble only has limited near-infrared capacities. The picture presents two views of the Eagle Nebula’s Pillars of Creation, as captured by Hubble. The left image is taken in visible light, whereas the right image is taken in infrared light, which pierces through much of the occluding dust and gas clouds to unravel hidden wonders. Credit: NASA/ESA/Hubble

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” this cloud of dust. A telescope optimised for infrared light would therefore allow us extend our vision into a hidden past world! Such ability would allow us to trace the earliest stages of stellar evolution.

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First mirror installation onto the James Webb Telescope. Credit: NASA

With such a magnificently profound instrument suite, the James Webb Telescope promises to push back the boundaries of our perception into a hidden world of vast cosmic wonders! If Hubble’s history is any indication, we are yet to imagine what the most powerful telescope ever built will unravel!

 

Featured image courtesy of NASA: JWST mirror segments undergoing cryogenic testing at the Marshall Space Flight Center.

 

 

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