Next-gen James Webb telescope will unveil mysteries of galaxy formation

Issued on: 12/12/2021 – 16:35

The James Webb Space Telescope, named after the former NASA administrator James Webb, will be launched on December 22 from Europe’s Spaceport in French Guiana, aboard an Ariane 5 rocket. Peering billions of years back in time, it promises to fill key gaps in our understanding of our Universe’s history.

“JWST will answer many questions from the edge of the universe. It will also allow us to study the atmospheres of planets in other solar systems in much greater detail than possible otherwise,” Mark McCaughrean of the European Space Agency and a member of the JWST Science Working Group, told FRANCE 24. 

Conceived more than thirty years ago and costing $9.7 billion, the telescope is an international collaboration between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). Europe has provided 1.5 of the four science instruments besides the Ariane 5 launcher.

One of the most striking features of JWST is its primary mirror, which is 6.5 metres in diameter and comprises 18 hexagonal segments. Once launched into orbit, these 18 movable segments will have to be aligned with extremely high precision (on the order of nanometres) to form the main mirror.

Equipped with a giant sun shield and four instruments that includes cameras and spectrographs, JWST will orbit the Sun at a distance of 1.5 million km from the Earth and make observations primarily at infrared wavelengths. 

“The earliest galaxies were formed so far back in time and so close to the Big Bang that by the time the light comes to us, it’s very faint and has been redshifted by the expansion of the Universe into the infrared. So you need a telescope which is powerful and which operates in the infrared – it also needs to be cold to avoid glowing in the infrared itself. JWST is all of those things,” McCaughrean says.

Imaging exoplanets

Among other important objects JWST will study are exoplanets i.e. planets orbiting distant stars beyond our solar system. While earlier missions have detected the presence of hundreds of such planets, JWST will go a step further by directly imaging some of them as well as performing spectroscopy of the atmospheres around them.  

One of the key instruments that will enable these measurements is called MIRI (for Mid-InfraRed Instrument)  which has been developed through a partnership between ESA, a consortium of European institutes, and NASA. MIRI consists of a camera, stellar coronagraphs and two spectrometers. The coronagraphs, developed by the LESIA lab at the Observatoire de Paris, drastically reduce the flux of bright objects compared to nearby faint ones. That will make it possible to observe exoplanets next to bright stars as well as the active centres of galaxies. 

Besides revealing the mystery on how galaxies in the early Universe were formed and imaging exoplanets, JWST will also peer into our own Milky Way galaxy enhancing our understanding of how young stars are born and how planets are formed around those stars. 

According to McCaughrean, JWST will also be an important component of multi-wavelength astronomy in which instruments operating in different wavelengths are trained on the same part of a sky for a comprehensive analysis of a phenomenon.

“For example, the Hubble Space Telescope has already taken extensive observations in the optical and ultraviolet of distant galaxies that JWST will follow-up in the infrared,” McCaughrean says. 

JWST’s impressive features are the result of several innovative technologies. “The main mirror of the Hubble Space Telescope is 2.4 metres across. JWST’s mirror is three times bigger, but the whole observatory only weighs half of Hubble. One of the main reasons why JWST is much lighter is because its mirrors are made out of beryllium and not glass,” he adds.  

The other crucial element of the observatory is its giant sunshield which will unfurl only after the observatory is launched into space. “The technology related to this five-layered sunshield, the size of a tennis court, had to be invented as it didn’t exist before.”  

Made of a specially coated lightweight material called Kapton, the diamond-shaped sunshield will help cool the telescope to a staggering -223°C. “You will have about 300 kilowatts of sunlight arriving on one side of the sunshield while on the other side where the telescope will be placed, you will have a few tens of milliwatts,” McCaughrean says.