Launch
After a long delay (the launch was originally due in 2007), the James Webb Space Telescope (JWST) was at last launched on December 25, 2021 by the powerful Ariane 5 rocket of the European Space Agency from its spaceport near Kourou, French Guiana.
The telescope is named after James E. Webb, the administrator of NASA from 1961 to 1968, who oversaw the creation of the Apollo program. (Originally, the telescope was named Next Generation Space Telescope.)
The JWST is an international collaboration between NASA, the European Space Agency, and the Canadian Space Agency.
Because of the efficient launch, NASA estimates that the JWST has enough propellant for a life of 20 years life, much longer than what was envisaged.
Position
On January 25, 2022, the JWST reached the second Lagrange point (L2) between the Earth and Sun, which is 1.5 million km away from the Earth, at which point it will orbit the Sun (unlike the Hubble Space Telescope which orbits the Earth). In this orbit, the telescope stays in line with the Earth as it moves around the Sun. (At Lagrange points, the gravitational pull of two large masses is precisely equal to the centripetal force required for a small object to move with them.) Webb’s position out at L2 also makes it easy for communication with the Earth.
Because of its position, the telescope’s ‘cold side’ that does the observing and its ‘hot side’ that carries the spacecraft’s solar panels and an antenna for two-way communication remain in their fixed direction, from the spacecraft’s point of view. The two sides are separated by a sunshield. According to NASA, in order to detect the infrared light from faint and very distant objects, the telescope itself must be kept extremely cold.
The JWST will not be stationary at L2 but will orbit around it. This orbit (one of which would be completed by the telescope in about 6 months) would keep the telescope out of the shadows of both the Earth and Moon. Unlike Hubble, which goes in and out of Earth shadow every 90 minutes, the JWST will have an unobstructed view that will allow science operations all the time, according to NASA.
After the telescope reached its position, it took another six months for the engineers and scientists to make it ready to do its work.
Mission
The JWST observatory will examine objects over 13.6 billion light-years away, or objects 13.6 billion years ago, i.e., some 100 to 250 million years after the Big Bang.
The JWST has a number of missions. They are as follows:
- It will be searching for the first light in the universe and the celestial objects which formed shortly after the Big Bang. One of its first tasks will be a survey, called COSMOS-Webb, of the most distant galaxies in a specific patch of sky, to explore conditions at the beginning of the universe.
- It will be investigating how galaxies formed and evolved. Supermassive black holes are known to exist at the centre of most galaxies. In the early stages of the universe, these black holes often powered enormously bright galactic nuclei called quasars, and six of the most distant and luminous examples of these are going to be studied by the JWST.
- The JWST will be observing the formation of stars from the first stages to the formation of planetary systems. The telescope will be able to penetrate the dust enveloping the stars at their beginning stages to reveal the secrets of star formation. Scientists may be able to learn something about the origins of the Sun and the solar system.
- The JWST will contribute to the search for exoplanets orbiting other stars, particularly Earth-like planets that may have the chemical ingredients and conditions necessary for life to evolve. The telescope will be using infrared imaging and spectroscopy to study the chemical and physical properties of planetary systems, and analyse the chemical composition of exoplanet atmospheres, looking in particular for signs indicating the building blocks of life.
Why Infrared Telescope
Ordinary optical telescopes see the same part of the spectrum as our eyes do, covering wavelengths between approximately 380 and 740 nanometres (nm). The Hubble telescope went a little beyond into the ultraviolet at shorter wavelengths and infrared at longer ones. The JWST, according to NASA, is optimised for 600 to 28,000 nm, making it an infrared telescope. As a result, it will be able to see only orange and red light and longer wavelengths, but will not be able to see green or blue light. This is useful in observing many astronomical objects, including star-forming regions, exoplanets, and the most distant galaxies as planets and newly formed stars tend to radiate at longer wavelengths.
An infrared telescope is best placed in space as Earth-based telescopes would have the problem of much of infrared being blocked by Earth’s atmosphere. The Earth produces its own infrared emissions via heat radiation, which tend to overwhelm the astronomical sources which are fainter. Also, while the dust in galaxies absorbs visible light, even sun-like stars are easier to see in the infrared despite a lot of intervening dust, according to NASA.
Important Components of the Telescope
The major components in the JWST are: (i) The integrated science instrument module (ISIM) houses four instruments to analyse the light that is captured by the optical telescope element or the mirror. (ii) The primary mirror segments are of gold-plated beryllium, the layer of pure gold intended to maximise reflectivity at infrared wavelengths. When all the 18 hexagonal mirror segments are put together, they form a diameter of 6.5m (21.3 feet) for the main mirror. There is a secondary mirror to guide the light collected by the primary mirror to the instruments. (iii) An enormous foldable sunshield is designed to protect the telescope from external sources of light and heat (like the Sun, Earth, and Moon) as well as from heat emitted by the observatory itself; the 5-layer sunshield is a critical part of the telescope because the infrared cameras and instruments aboard must be kept very cold and out of the Sun’s heat and light to function properly. (iv) The spacecraft bus contains all the equipment for the operation of the observatory.
The tools that collect the data are: (i) the mid-infrared instrument (MIRI) which provides imaging and spectroscopic observation for radiation with wavelengths from 4.9 to 28.8 micrometres; (ii) the near infrared camera (NIRCam) focused on wavelengths of light from 0.6 to 5.0 micrometres, and which is also used for JWST mirror alignment; (iii) the near infrared imager and slitless spectrograph (NIRISS) that observes at wavelengths between 0.6 and 5.0 micrometres; and (iv) the near infrared spectrograph (NIRSpec) which provides spectroscopy from 0.6–5.3 micrometres.
The First Images and Findings
In July 2022 the much awaited first images captured by the JWST were released by NASA.
The telescope had delivered the deepest and sharpest infrared image of the distant universe so far, said NASA. The image was of galaxy cluster SMACS 0723, known as the telescope’s First Deep Field, and full of thousands of galaxies–including the faintest objects ever observed in the infrared. The image showed SMACS 0723 as it appeared 4.6 billion years ago, with many more galaxies in front of and behind the cluster. This deep field was taken by the near-infrared camera (NIRCam) on the telescope bringing the far-off galaxies into sharp focus. This field was also imaged by the telescope’s mid-infrared instrument (MIRI). NIRISS captured spectra of all the objects in the entire field of view. It showed one of the galaxies to have a mirror image.
Later in July, it was reported that astronomers, analysing data from the Grism Lens-Amplified Survey from Space (GLASS), believed they had found the oldest galaxy ever imaged—one dating back 13.5 billion years, or just 300 million years after the Big Bang. In other words, it means seeing something as it looked 13.5 billion years ago. The galaxy was dubbed GLASS-z13. A team of scientists detected this on the basis of the red shift shown by the galaxy. The age of a galaxy is measured by what is known as its red shift: with the expansion of the universe, the wavelength of light stretches into the red spectrum. The redder the image, the greater the stretching and the farther and older, the object is. The 13 in GLASS-z13 signifies the redshift of the galaxy; a higher redshift indicates that the galaxy is farther away from the Earth. The galaxy is said to measure 3,000 to 4,500 light-years across and has about a billion stars–which is not much compared to our galaxy, the Milky Way, which measures about 100,000 light-years across and contains an estimated 200 billion stars.
Before the JWST was launched, the most distant confirmed galaxy known was GN-z11, which astronomers said dated to about 420 million years after the Big Bang.
As research goes on, yet another galaxy, even older than GLASS, was reported to have been discovered later by researchers who said the galaxy could have been formed 250 million years after the Big Bang.
One of the other images was that of the Carina Nebula in close up. The Carina Nebula is a bright and gassy hotbed of star formation which is approximately 7,600 light-years from the Earth. Though the nebula has been studied earlier, the new image reveals in much greater than ever before the ‘mountains’ and ‘valleys’ of a star-forming region called NGC 3324 in the nebula, known as the ‘cosmic cliffs’ of Carina. Through the gassy landscape of the nebula can be seen hundreds of newborn stars that telescopes had not been able to see before. The Carina Nebula is home to some huge stars, several of them much larger than the Sun.
Another image is that of the Southern Ring Nebula, or ‘Eight-Burst Nebula’, which is a cloud of gas and dust shaped like the figure 8. The gas and dust were being expelled by a massive, dying star some 2,500 light-years from the Earth. Investigating the molecules present in such stellar graveyards can help scientists learn more about the process of stellar death.
Also revealed were fresh details of Stephan’s Quintet, a cluster of five galaxies four of which experience repeated close encounters; these provide insights into how early galaxies formed at the start of the universe. The JWST was able to capture the shockwaves as one of the galaxies smashes through the centre of the cluster. Stephan’s Quintet is located some 290 million light-years away. It was the first compact galaxy group ever discovered way back in 1877 and will be the furthest image taken by the JWST.
Another finding related to the presence of water vapour in the atmosphere of a gas planet outside our solar system, is WASP-96 b. The spectroscopy revealed detailed information about the planet, which was discovered in 2014. WASP-96 b is about 1,150 light-years from the Earth and is about half the mass of Jupiter; it orbits its star in just 3.4 Earth days.
Other images related to a spectrum image of a nearby alien exoplanet, revealing the precise chemical composition of the planet’s atmosphere, and close-ups of enormous, dust-shrouded objects located throughout the universe.
Astronomers from around the globe will be able to get shares of time on the telescope, once their applications and projects are selected competitively through a process in which applicants and selectors are not aware of each other’s identities so as to minimise bias.
Incidentally, the spectacular colours in the images are artificial as the actual images are monochromatic.
How the JWST Differs from the Hubble
The JWST is considered as an improved successor to the Hubble telescope which was launched way back in 1990. There are some vital differences between them.
The Hubble focus is on visible and ultraviolet light. Though it can observe a very small portion of the infrared spectrum, it cannot match the JWST in the extent of coverage; the JWST will be able to focus on bright objects like very distant galaxies. The JWST, on the other hand, being specifically designed to focus on the infrared spectrum, cannot see in ultraviolet light.
The James Webb Telescope is also much larger than the Hubble, mostly due to its large sunshield. Though all space telescopes have sunshields, the one on the JWST is very important because of the infrared cameras. If the spacecraft is not kept cool, it could risk being blinded by the lights of objects it is trying to observe.
The Hubble orbits the Earth above Earth’s atmosphere but is near enough to be approached if repairs needed to be done. The distance of the JWST is some 1.5 million km from the Earth, so anyone going over to repair anything is out of the question.
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