nebulae, exoplanet, group of galaxies... discover all his first images

nebulae, exoplanet, group of galaxies… discover all his first images

FactualThese objects illustrate the versatility of JWST’s infrared astronomy. As they are unveiled, they can be compared with the results of its predecessors, Hubble and Spitzer.

The American (NASA), European (ESA) and Canadian (ASC) space agencies unveiled on Tuesday July 12 the first images taken by the largest space telescope, the James-Webb (JWST), launched in December 2021 by an Ariane 5 rocket. They concern five different regions of the sky and were chosen to illustrate the unprecedented performance of the instrument, in comparison with its predecessors, Hubble and Spitzer. Here are these objects as they had never been seen before, compared to the way they were known to us before the advent of the James-Webb.

Here are these images with comparisons taken from shots taken by Hubble or Spitzer, which was exploited between 2003 and 2020 and which, like JWST, sees in the infrared. This wavelength makes it possible to observe more distant objects, because the wavelengths of the lights they emit are lengthened by their distance, like the sound of the siren of an ambulance leaving a hospital. It also makes it possible to see through the interstellar dust that populates the galaxies, to the point of making them invisible to Hubble, for example. The colors of the JWST images are therefore “false”in the sense that the real, invisible wavelengths have been shifted to be visible to the eye in the photos.

Of the four instruments, two can take images, MIRI and NIRCam, with different calibrations which explain the different colors.

Deep field, SMACS 0723

Image of the deep field of the Universe taken by the James-Webb telescope, unveiled on July 11 at the White House by President Joe Biden.

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.

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