Last year, University of Melbourne, Australia, researchers collaborated with the US space agency Nasa on a study to understand, through computer simulations, just how powerful the James Webb Space Telescope could be. It showed that the Webb, which is set to be launched on 24 December, will let us study the host galaxies of distant quasars (the extremely luminous cores of these galaxies). Why is that a big deal? According to Nasa, looking at a quasar and its host galaxy is like “looking directly into a car headlight and trying to figure out what kind of automobile it is attached to”—so far, it has been near impossible for scientists to study them.
An international collaboration between Nasa, the European and Canadian space agencies, the $10 billion ( ₹760 billion) space telescope, named after former Nasa administrator James E. Webb, has been in the works for decades. Finally, it’s set for launch on Ariane flight VA256, from the ELA-3 launch pad of the Guiana Space Centre in French Guiana, on the northern Atlantic coast of South America. Once in space, the telescope will be situated near the second Lagrange point of the Earth-Sun system, around 1,500,000km from Earth, directly opposite the Sun.
Why should we care about the James Webb Space Telescope?
The Webb, the most powerful and complex space observatory, will allow us to look deeper into our solar system than ever before. It will allow us to traverse space and time, in a way, because not only will it give us a clearer view of exoplanets in the solar system than we have ever had access to, it will also help us understand how the universe itself was formed; indeed, some people are calling it “a $10 billion time machine”. The Webb is also a key component of the search for extraterrestrial life: One of the aims of the scientific community is to get detailed atmospheric characterisation of potentially habitable exoplanets.
“There is a palpable sense of impatient excitement (within the scientific community),” says Poshak Gandhi, professor of astrophysics at the University of Southampton, UK, on email. For the Webb could provide findings useful for many scientific communities.
Gandhi, for instance, is leading the JWST Timing Consortium, a global team of experts focused on exploiting JWST’s rapid time-domain capabilities. “In the JWST Timing Consortium, we will use this new capability to effectively create ‘movies’ of growing black holes in our galaxy,” he says. “Black hole environments are chaotic, subject to extreme gravity and very fast motions of interstellar gas. We will use JWST to study this chaos to understand how black holes grow in times as short as a fraction of one second.”
How does it work as an eye in the sky?
The Hubble telescope, in operation for over 30 years, has been useful in spotting faraway galaxies and telling us more about the universe’s age and expansion. The JWST is expected to go much further. A big reason for this is the astounding technologies it will carry. This includes a big primary mirror, 6.5m across and made of 18 hexagonal segments. The focus of the mirror can be calibrated by shifting the various segments.
The telescope works in the infrared spectrum, collecting infrared light from the object it is focused on. Essentially, by focusing and then projecting this light on to infrared detectors, which will convert the photons in the light to electrical voltage and then project them on to the imaging devices within the telescope.
Why the infrared spectrum?
Owing to what is called “the red shift” in astrophysics, light travelling immense distances goes through a lengthening of the waves and becomes infrared, making it easier to trace its origin. Additionally, “cold” objects such as debris disks and planets emit most strongly in the infrared, and this band is difficult to study from Earth because of interference from our atmosphere and its particles. The JWST’s near-infrared astronomy capabilities are far stronger than that of the Hubble, which is optimised for visible light.
“Our eye sees light of wavelength 0.4-0.8 microns. The Hubble telescope has been sensitive to wavelength 0.1-1.8 microns (0.1-0.4 is in the ultraviolet, or UV, wavelength and is stopped by Earth’s atmosphere). So, the Hubble has given us a unique UV view of the universe in addition to images corresponding to normal optical light,” says Somak Raychaudhury, director of the Inter-University Centre for Astronomy and Astrophysics in Pune, Maharashtra, on email. “The JWST will observe mostly in the near-infrared, or IR, almost entirely outside the visual range—the other side of the spectrum from Hubble,” he adds. “The imager and spectrograph in the near-IR will open up new windows of light to us. Such capability has not been available from a space platform before.”
How far will it be able to see?
The Webb’s infrared vision will be able to look back over 13.5 billion years to see the first stars and galaxies of our early universe. One of its other key scientific goals is to look at other planetary systems, understand more about exoplanets, and perhaps even find signs of life in the universe. “If you compare it (JWST) with the Hubble, the technology and instruments have had major upgrades—the imagers, cameras, spectrometers. Space telescopes have played a very pivotal role in finding planets in other solar systems that have conditions conducive for life to have existed,” says Siddharth Pandey, head of the Centre of Excellence in Astrobiology at Amity University, Mumbai. “Over the last 20 years, we have seen a significant increase in the discovery of these kinds of planets. It has reached a point where we need to observe them better. With the launch of the Webb, we will be able to make more detailed observations of the atmosphere of such planets. That’s something exciting from an astrobiology point of view,” adds Pandey.
What could go wrong?
The Webb has as many complications as advantages. Perhaps one of the biggest challenges is that once it is deployed, it will be almost impossible to make any physical repairs on it; in contrast, the Hubble had its fifth and final servicing mission in 2009. That’s because the Hubble Space Telescope orbits Earth at an altitude of 570km above it. The Webb will be roughly 1.5 million kilometres away.
Even the mission to launch it is highly complicated. As Nasa explains in a fact-sheet, the Webb’s enormous size and frigid operating temperature present “extraordinary engineering challenges”. After launching from French Guiana, the observatory will travel to its orbit around the L2 point. It will then undergo six months of commissioning, which involves unfolding its mirrors, sunshield and other smaller systems, among other functions.
The margin of error is so small that its launch was moved ahead by a few days after a minor incident in November when technicians tried to attach it to its launch vehicle. This sent “minor vibrations” through the telescope.
For now, as Gandhi says, it’s fingers crossed for a successful launch and orbital deployment. He adds: “Looking back at successful telescopes such as Hubble and Chandra (X-ray Observatory), their best discoveries have often come from unforeseen lines of investigation. Whenever new parameter space is opened up with new telescopes, this allows for new research that was not originally foreseen in the mission design. So, JWST’s legacy may ultimately be something that we have not even thought of yet.”