Home LATEST NEWS Journey to the Middle of Webb’s Deep Field

Journey to the Middle of Webb’s Deep Field

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The answer is short but evocative: thousands of galaxies – including some of the most distant which appear to us for the first time thanks to the NIRCam and MIRI instruments of the James Webb telescope. These two imagers, supported by the Canadian precision guidance detector which makes it possible to point towards a target with extreme precision, observe the Universe in the near and mid-infrared. These wavelengths pass through dust clouds and reveal celestial objects that have remained invisible to other telescopes such as Hubble.

Comparison between images of the galaxy cluster SMACS 0723 taken by Webb and Hubble.  Bright spots on a dark background appear much more numerous in Webb's image.

Galaxy cluster SMACS 0723 as seen by Webb (left) and Hubble (right).

Photo: NASA/ESA

Let’s start by recalling 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 little grain of sand between two fingersrecalls André Grandchamps.

The image shows the galaxy cluster SMACS 0723. The galaxies that form this cluster lie towards the center of the image and take on the appearance of hazy whitish circles with some cloudiness around in shades of graynotes the astrophysicist.

Bright dots on a dark background.

The galaxies in the cluster correspond to the fuzzy white patches, some of the brightest of which are in the center of the image.

Photo: NASA/CSA/ESA

They should not be confused with the stars that are in the foreground of the image.

The celestial bodies which appear with six bluish lines around them are stars of our galaxy which are in our field of vision, between the cluster and usnotes Mr. Grandchamps.

A shining star under dark background.

Stars of our galaxy are in our field of vision, between the cluster and us.

Photo: NASA/ESA/CSA

If these stars of the Milky Way are a few tens of thousands of light-years away, the galaxies of the cluster are much further away at around 4.6 billion light-years from Earth. »

A quote from André Grandchamps, astrophysicist at the Rio Tinto Alcan Planetarium

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 space-time around it. This gravitational lensing effect amplifies the light emitted by the more distant galaxies behind it. They appear in the image as darker, often stretched orange spots around the cluster.

Close-up of a distant galaxy surrounded by two galaxies in the SMACS 0723 cluster.

Close-up of a distant galaxy surrounded by two galaxies in the SMACS 0723 cluster.

Photo: NASA/CSA/ESA

You have a nice example of this to the right going 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. »

A quote from André Grandchamps, astrophysicist at the RioTinto Alcan Planetarium

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 image, is estimated at 13.1 billion light-years.

The orange dot located at the bottom left of the center corresponds to a galaxy located 13.1 billion light-years away.

The orange dot located at the lower left of the center corresponds to a galaxy located 13.1 billion light-years away.

Photo: NASA/ESA/CSA

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 instrument (for imager and spectrograph without slit in the near infrared) makes it possible to study celestial objects in order to establish their composition, but also to measure their distance.

By breaking down the light emitted by a celestial object using spectroscopy, it is possible to know its composition and distance. It’s that each chemical element in the Universe has different characteristics, a kind of chemical fingerprint. For example, the characteristics of hydrogen are different from those of helium and lithiumexplains Mr. Grandchamps.

The lens effect can sometimes create a mirror effect. The phenomenon is observable to the left and to the right of the central cluster. It is possible to see each of the galaxies twice, which forms luminous arcs. Additionally, Webb’s image distinctly reveals their bright, star-filled cores, as well as the orange stellar clusters along their edges.

These arcs are mirror images of the same galaxy whose light was emitted 9.3 billion years ago.

These arcs are mirror images of the same galaxy. The arc light to the left of the center blue line (initial image) was emitted 9.3 billion years ago.

Photo: NASA/ESA/CSA

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 compositions. 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 vertical bluish line of the center star, to the right of a long orange arc. You can see pockets of forming stars reflected from top to bottom.

The speckled galaxy appears in the center of the image.

The speckled galaxy appears in the center of the image.

Photo: NASA/ESA/CSA

The deep field also reveals many types of galaxies, such as a spiral galaxy, visible to the right of the original image.

This galaxy is of the spiral type, like our Milky Way.

This galaxy is of the spiral type, like our Milky Way.

Photo: NASA/ESA/CSA

Even closer to the big bang

Webb’s Deep Field shows the same star cluster as seen with the Hubble Telescope.

It’s completely voluntary because we wanted to compare the two telescopes. With just 12 hours of exposure, Webb got about 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 obtain with the same exposure time! »

A quote from André Grandchamps, astrophysicist at the RioTinto Alcan Planetarium

Webb’s technical abilities 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 great formative boom of the Universe.

We had never had instruments that allowed us to hope to see them, it is now possible. We know they appeared one day because we are here todayenthuses André Grandchamps.

He uses this parallel to illustrate the work that scientists wish to accomplish: Imagine aliens arriving on Earth and encountering only adult humans. They will wonder where we come from! They will eventually find a daycare and a nursery and understand our evolution. Finding the (primordial) nursery of stars is kind of what Webb is working on. It is certain that we see more adult stars and galaxies because they spend more time of their evolution in their “adult life”.

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