The answer is short but evocative: thousands of galaxies – including some of the most distant ones, which are appearing to us for the first time thanks to the NIRCam and MIRI instruments of the James Webb Telescope. These two imaging cameras, supported by the Canadian Precision Guidance Detector, which enables pinpointing of a target with extreme precision, observe the universe in the near and mid-infrared. These wavelengths pass through dust clouds and reveal celestial bodies that have remained invisible to other telescopes such as Hubble.
Let’s start by keeping in mind that the photograph corresponds to a very small part of the sky in the southern hemisphere, located in the constellation of the Flying Fish.
It’s like holding up a small grain of sand between two fingersremembers André Grandchamps.
The image shows the galaxy cluster SMACS 0723. The galaxies that make up this cluster lie towards the center of the image and look like
hazy whitish circles with some cloudiness around in shades of graynotes the astrophysicist.
They are not to be confused with the stars that are in the foreground of the picture.
The celestial bodies shown with six bluish lines around them are stars in our galaxy, which are in our field of vision, between the cluster and usnotes Mr. Grandchamps.
” If these stars in the Milky Way are a few tens of thousands of light-years away, the cluster’s galaxies are much further away at about 4.6 billion light-years from Earth. »
The light that these galaxies send back was therefore emitted shortly before the formation of our planet.
A cluster like a magnifying glass
The sheer mass of the cluster distorts the spacetime around it. This gravitational lensing effect amplifies the light emitted by the more distant galaxies behind. They appear in the image as darker, often stretched orange spots around the cluster.
” You have a good example of this on the right to go to the top of the image. The two whitish dots are two cluster galaxies. The sort of flattened orange ridge in between is a distant galaxy. »
The distance to this orange ridge is not yet known, but several galaxies that lie behind the cluster are between 11 and 13 billion light years from Earth.
Most small orange galaxies are very far away. The distance of one of them, which is practically not visible in the full picture, is estimated at 13.1 billion light years.
Mr. Grandchamps adds that the very small orange dots are not necessarily the most distant.
They can also belong to objects that are inherently small. To know if an object is very far, it must be evaluated.
The Canadian NIRISS (Near Infrared Imager and Slitless Spectrograph) instrument allows celestial bodies to be studied to determine their composition, but also to measure their distance.
By breaking down the light emitted by a celestial body using spectroscopy, it is possible to know its composition and distance.
It is that each chemical element in the universe has different properties, a kind of chemical fingerprint. For example, the properties of hydrogen are different from those of helium and lithiumexplains Mr. Grandchamps.
The lens effect can sometimes create a mirror effect. The phenomenon can be observed to the left and to the right of the central cluster. It is possible to see each of the galaxies twice, forming luminous arcs. In addition, Webb’s image clearly reveals their bright, star-filled cores as well as the orange star clusters along their edges.
The two flattened orange lines, which are above the other, at the bottom of the image, have the same spectral signature, therefore have the same chemical composition. They probably belong to the same galaxynotes André Grandchamps
It is also possible to see a galaxy speckled with star clusters; it is located near the end of the central star’s vertical bluish line to the right of a long orange arc. You can see pockets of forming stars reflected from top to bottom.
The deep field also reveals many types of galaxies, such as a spiral galaxy visible to the right of the original image.
- It was US President Joe Biden who unveiled the now historic image at an event held on July 11 at the White House, six months after James Webb was launched into orbit.
- The James Webb Telescope’s deep field is the eighth of its kind released since 1995. It is the Hubble Telescope that returns the feat with the very first deep field. The instrument picked up four others, the last of which (extremely deep field) dates back to 2012. The other deep fields were taken using the Chandra telescopes (1999) and the European Southern Observatory’s Very Large Telescope (2012).
Even closer to the big bang
Webb’s Deep Field shows the same star cluster as seen with the Hubble telescope.
” It is completely optional because we wanted to compare the two telescopes. With just 12 hours of exposure, Webb got as good a picture of very distant objects as Hubble could in 100 hours. We can now dream of the results that the Webb telescope will achieve with the same exposure time! »
Webb’s engineering skills would make it possible to go back in time and perhaps see the first galaxies and stars that formed between 500,000 years and a billion years after the universe’s great formative boom.
We had never had instruments that allowed us to hope to see them, it is now possible. We know they showed up one day because we are here todayenthuses André Grandchamps.
He uses this parallel to illustrate the work that researchers want to do:
Imagine aliens arriving on Earth and meeting only adult humans. They will wonder where we come from! They will eventually find a daycare and a nursery and understand our development. Finding the stars’ (primordial) nursery is one of the things Webb is working on. It is certain that we see more adult stars and galaxies because they spend more time of their development in their “adult lives”.