The American (NASA), European (ESA) and Canadian (ASC) space agencies will unveil on Tuesday July 12 the first images taken by the largest space telescope, the James-Webb (JWST), launched in December 2021 by an Ariane rocket. 5. They concern five different regions of the sky and have been chosen to illustrate the unprecedented performance of the instrument, in comparison with its predecessors, Hubble and Spitzer. Before the curtain goes up, here is a presentation of these objects, and a sample of how they were known to us before the advent of the James-Webb
Deep field, SMACS 0723
For this first image, the suspense is over. US President Joe Biden has indeed broken the embargo agreed with the European and Canadian space agencies to present it in preview, Monday July 11, from the White House, before a tour of the Middle East. We see an impressive cloud of multicolored light spots on a black background. They are hundreds, even thousands of galaxies, concentrated in a very small portion of the sky, equivalent to the size of a grain of sand at the end of an arm.
From one of these galaxies, white on the right, we can clearly see the spiral arms, almost indistinguishable for Hubble, which had taken the same shot. The image also strikes with very white dots with eight “branches”. These are stars in our galaxy within the telescope’s field of view. The “branches” betray the particular geometry of its mirror made up of 18 hexagons: the light diffracts on the tiny borders between them and creates these particular figures.
Other points are also remarkable, essentially massed in the center, under the brightest star. It is a compact cluster of galaxies, SMACS 0723, more than 4 billion light-years from Earth, and which explains the presence of orange arcs in the photo. Its enormous mass distorts spacetime and bends light rays in its vicinity, especially those coming from the background. So that JWST sees several images of the same galaxy located behind the cluster. If it were exactly aligned behind, we would see a perfectly circular ring. The interest is that it amplifies this distant light and therefore makes it possible to see even more distant objects. “It’s like a second telescope”explains Johan Richard, astronomer at the astrophysical research center of the Lyon observatory.
This is where JWST reveals that he is a time machine: he sees objects whose light took more than 13 billion years to reach us, while the Big Bang took place 13 years ago. .8 billion years. Astronomers will therefore be able to see and study the very first stars and galaxies in the Universe, and push back the limits reached by Hubble.
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