Each picture offers “to humanity a view of the universe we have never seen before”. These words from Bill Nelson, head of the American Space Agency (Nasa), sum up the value of the first images from the James Webb Space Telescope, unveiled on Tuesday July 12 with great fanfare. This publication marks the beginning of the scientific operations of the most powerful space telescope ever designed, awaited for years by astronomers around the world.
But what exactly do we see in these beautiful images of stars and galaxies? To help you understand them, franceinfo asked astrophysicists Anthony Boccaletti and Eric Lagadec to decipher them. “These are objects already observed, but in a different way”explains the first. “These images just serve to show that this instrument has enormous potential, it’s the beginning of a new era”estimate the second.
a mistress of the galaxies
The first snapshot, unveiled by US President Joe Biden on Monday, shows a cluster of galaxies, called SMACS 0723. “You have to imagine three different planes: the very bright stars, which form crosses, are in our galaxy. Then you see a supermassive cluster of white-colored galaxies, and the orange objects are distorted images of more distant galaxies”exhibits Anthony Boccaletti, from the Paris Observatory.
By acting as a magnifying glass, the cluster of white galaxies makes it possible to reveal very distant cosmic objects located behind it, an effect called gravitational lensing. “The redder these galaxies are, the further away they are and the more we see it in a time close to the Big Bang”more than 13 billion years ago, adds Eric Lagadec. The astrophysicist from the Côte d’Azur Observatory uses an image to help us better understand these celestial objects: “What we see represents a part of the sky so small that it could be hidden by a grain of sand held at arm’s length”. On Twitter, he also compares it to a previous photo, taken by the old Hubble telescope, which makes it possible to realize the precision of James Webb.
Let’s start with a comparison: on the left an observation by the Hubble telescope, on the right the first image of the JWST. The bright dots with crosses are stars in our galaxy. Everything else is galaxies. pic.twitter.com/c9kSN9jhlJ
— Eric Lagadec (@EricLagadec) July 12, 2022
Stephan’s Quintet is a compact grouping of galaxies, 290 million light-years away. white objects “are five interacting galaxies, which are interacting and dancing around each other”explains Eric Lagadec. “This helps highlight star-forming regionscompletes Anthony Boccaletti. What you see in red is the gas and dust that form stars.”.
The Carina Nebula
This image shows what a star forming zone looks like from close : a gigantic cloud of dust and gas. This Carina Nebula is located about 7,600 light-years away. It is cut into two parts. Below, an orange area where “we see gas, dust and stars forming“, describes Eric Lagadec. At the top, a blue zone, “where we see stars already formed, which radiate and create places without gas”. “Not all the colors you see here are real, the telescope sees ranges you can’t see with the naked eye, you have to interpret the light”continues Anthony Boccaletti, specifying that there is “a whole aesthetic work” behind.
A dying star
These two images, taken by two different instruments of the James Webb Telescope, show the Southern Ring Nebula, which surrounds two stars, one of which is dying. “When a star dies, it ejects gas and dust, that’s what we see in this image”deciphers Eric Lagadec. The structure of the nebula, “in the shape of a diabolo”betrays the presence of a second, smaller star, which can be seen on the visualization on the right.
The spectrum of an exoplanet
This is the least spectacular image of this first delivery and for good reason: it is a spectrum, an analysis of the light emitted by an object to determine its chemical composition. In this case, the exoplanet – ie a planet outside our solar system – WASP-96 b. “By observing its main star, we manage to detect a small modification of the light when the planet passes in front of it and this allows us to have information on its atmospheric composition”explains Anthony Boccaletti. The astrophysicist, however, wants to temper the excitement that could arise around the mention “water” (water) on this graph: this water is not in liquid but gaseous form, which does not have the same potential at all. in terms of life development.