Last night, President Biden presented the first image taken by the James-Webb Telescope or JWST (its English acronym). Since its launch on December 25, 2021, and even before, the community of astronomers and astrophysicists has been very impatient. And there is reason, because this telescope promises major advances in astronomy, particularly in the study of the origins of the universe or exoplanets.
Take pictures of the origins of the universe
In the photo taken by the JWST, we see a lot more as shown in the comparison below. The bright dots with crosses are stars in our galaxy. These “peaks of light” are due to the configuration of the telescope mirror, segmented into small hexagons. Everything else is galaxies. On the other hand, the biggest difference lies in the time it takes to take it. It took several weeks for Hubble to produce this image, but only twelve and a half hours for Webb. This is due to the large size of its mirror, collecting more light faster.
Some of the galaxies visible in this image are 13 billion light-years away. This means that light has taken 13 billion years to travel to us since it was emitted from the galaxy, meaning that we see the universe as it was shortly after the Big Bang. If this could have been possible with Hubble, the James-Webb telescope has a much better resolution, making it possible to detect the shapes of galaxies in a much more detailed way.
These galaxies are of various morphologies and colors. The colors tell us about their distances, the furthest being those with the longest wavelength, therefore the reddest. These are also simpler forms, less structured, because they are "younger". Galaxies take on increasingly complex shapes as they interact with other galaxies.
There is still a huge field to photograph with the Webb, because the part of the universe that we see in this image is tiny: we could hide it by holding a grain of sand at arm's length.
Infrared to understand the formation of galaxies
One of the big differences between Hubble and the Webb is their spectral range: Hubble sees mainly in the visible while the Webb is an infrared telescope. Stars near the Big Bang, although long dead, emitted ultraviolet radiation. Their distance, due to the expansion of the universe, shifts their wavelengths towards the infrared.
The Webb will also make it possible to observe the Stardust. This substance exists in two forms: carbonaceous, similar to soot, and in the form of silicate, resembling sand. It forms around stars at the end of their life, then passes through the interstellar medium, ending by forming new stars. And eventually, new galaxies.
This dust has the crucial property of being visible in the infrared and opaque in the visible, making it impossible for Hubble to analyze it. The Webb's observation of dust should lead to a better understanding of the mechanisms of formation of stars and galaxies. This will be done in particular by observing the Carina Nebula, the Austral Ring Nebula and Stephan's Quintet.
Finally, the images from the Webb telescope, freely accessible to scientists and the general public, will make it possible to examine exoplanets and their atmosphere. Indeed, several molecules are observable in the infrared – the water molecule for example.
This article is part of the series "The great stories of science in open access", published with the support of the Ministry of Higher Education, Research and Innovation. For more information, please visit the page Openthescience.fr.