The James Webb Telescope took us 13 billion years in the past

Last night, President Biden presented the first image taken by the James Webb Telescope, or JWST (its acronym in English). Since its launch on December 25, 2021, and even before that, the community of astronomers and astrophysicists has been extremely impatient. And there is a reason, because this telescope promises to bring about major advances in astronomy, particularly in studying the origins of the universe or exoplanets.

Take pictures of the origins of the universe

In the photo taken by JWST, we see a lot as shown in the comparison below. Bright spots with crosses are stars in our galaxy. These “peaks of light” are due to the composition of the telescope’s mirror, divided into small hexagons. Everything else is galaxies. On the other hand, the biggest difference lies in the time it takes. It took Hubble several weeks to produce this image, but only twelve and a half hours for Webb. This is due to the large size of its mirror, which collects more light faster.

Some of the galaxies visible in this image are 13 billion light-years away. This means that the light has taken 13 billion years to travel to us since it was emitted from the galaxy, which means that we see the universe as it was shortly after the Big Bang. If this is possible with Hubble, the James Webb Telescope has a much better resolution, which makes it possible to discover the shapes of galaxies in a much more detailed way.

These galaxies have different shapes and colors. The colors tell us their distance, the farthest being those with the longest wavelength, and therefore the redder. These are also simpler and less structured forms because they are “younger”. Galaxies take on increasingly complex shapes as they interact with other galaxies.

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There is still a huge scope for Webb imaging, because the part of the universe we see in this image is so small: we can hide it by holding a grain of sand at arm’s length.

Infrared to understand the formation of galaxies

One big difference between Hubble and Webb is their spectral range: Hubble sees mainly in the visible while Webb is an infrared telescope. Stars near the Big Bang, although long dead, were emitting ultraviolet radiation. After them, due to the expansion of the universe, they change their wavelengths towards infrared radiation.

Webb will also make it possible to observe star dust. This substance exists in two forms: carbonate, similar to soot, and in the form of sand-like silicate. It forms around stars at the end of their lives, then passes through the interstellar medium, ending Forming new stars. And finally, new galaxies.

This dust has the primary characteristic of being visible in the infrared and opaque in the visible, making it impossible for Hubble to analyze it. Webb’s observation of the dust should lead to a better understanding of the formation mechanisms of stars and galaxies. This will be done in particular by observing the Carina Nebula, the Austral Ring Nebula and the Stephan Quintet.



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Finally, images from the Webb Telescope, which are freely accessible to scientists and the general public, will make it possible to examine exoplanets and their atmospheres. In fact, many molecules can be observed in the infrared – a water molecule for example.


This article is part of the “Great Science Stories in Open Access” series, published with the support of the Ministry of Higher Education, Research and Innovation. To find out more, please visit the page Openthescience.fr.

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