There are a multitude of white dots, others rather orange and some that emit a bluish glow.

This is the composition of the very first image of deep space taken by the James-Webb telescope and made public by US President Joe Biden on Monday July 11.

A snapshot that is a foretaste for the images that NASA is to unveil on Tuesday.

"This is a historic moment for science and technology," said the American president before adding that this snapshot shows that "we can go places where no one has ever been".

But where does the telescope commissioned on December 25, 2021 take us precisely with this image?

From its orbit 1.5 million kilometers from Earth, it sent a view of "the cluster of galaxies SMACS 0723 as it existed 4.6 billion years ago", explains NASA in a Press release.

This is indeed the time it took for the light emitted by these galaxies to reach the sensors of the James-Webb telescope, which means that the published image represents a snapshot of this part of the universe at this remote era.

It is a small corner of the sky "no bigger than a grain of sand held at arm's length" in the vastness of the universe that is located in the constellation of the Flying Fish, one of the largest small visible from the southern hemisphere.

A time machine

But this is only a very small part of the story that this photo tells.

First, this is not the first time that a telescope is interested in this specific place in the universe.

In 1995, Hubble was already taking a snapshot of the same area and the comparison between the two images shows how Hubble's successor gives, nearly 30 years later, a much more abundant version of this parcel of space.

Before and after.



Here's what the Hubble Space Telescope -- until now the benchmark in space-based astronomy -- saw of galaxy cluster SMACS 0723 in a sliver of the southern sky.



Continue watching to see the new view from the James Webb Space Telescope.https://t.co/WJmoIqMAMl pic.twitter.com/f8W2l5ftUV

— Spaceflight Now (@SpaceflightNow) July 12, 2022

A much more detailed vision which is not only due to the size of the Webb telescope, three times larger than its predecessor.

"This is mainly due to the fact that Hubble only captured what is visible to the naked eye while the James-Webb telescope perceives the infrared signature of space objects", explains Anthony Boccaletti, astrophysicist at the Paris-PSL Observatory. and research director at the CNRS.

Indeed, the farther a star, a planet or a galaxy is from Earth, the more the light it emits goes out of the spectrum of what is visible to the naked eye to enter the infrared range.

This is why Hubble would never have been able to "see" the outer reaches of space, and this ability to perceive infrared makes the James-Webb Telescope the ideal device for exploring the early days of the universe.

But all that is visible on this first historical image is not at the same distance from the Earth… Far from it.

Everything is, in fact, in the color code.

"The bluish dots represent, for example, the stars, which are much closer to us than the rest", notes Anthony Boccaletti.

They are "only" a few hundred million light-years away.

These stars are also quite few in the photo.

"This may be one of the reasons why the telescope photographed this area," suggests Anthony Boccaletti.

Indeed, the more stars there are, the more their light – more intense than the rest – was likely to hide the forest of galaxies behind.

A forest made up of a large number of points, which are all different galaxies.

"What we see, in reality, are two clusters of galaxies. The closest is made up of rather white points, while all that is orange represents the second set of galaxies", describes the astrophysicist.

Waiting for images of exoplanets

There is therefore not only SMACS 0723 on this image.

The orange galaxies in the background date back even further, potentially a few billion more years.

Some of the more distant shapes also appear as distorted, which is related to the mass of SMACS 0723 galaxies. The "heavier" a space object is, "the more it distorts the space-time around it for the observer", explains Anthony Boccaletti.

This is what gives this luminous signature in the form of an arc of a circle for certain galaxies.

"It is by measuring the deformation of space-time that scientists can, for example, estimate the mass of galaxies", specifies the researcher from the Paris Observatory.

A firework of details all the more extraordinary as this first shot was obtained after an exposure time of "only" 12.5 hours. less precise of this area of ​​the universe.

What reinforce the hopes of the scientists as for the exploration of the first times of the universe, which go back to 13,8 billion years.

"The longer the exposure time, the more the telescope will be able to capture the weakest light signals that correspond to the signature of the youngest stars", summarizes Anthony Boccaletti.

This first demonstration of the capabilities of the James-Webb telescope is also encouraging for its other major mission: to collect information on exoplanets.

"This confirms that it should allow us to probe their atmosphere in order to learn more about their composition", notes Anthony Boccaletti, whose specialty is the study of exoplanets.

So far, almost all of what is known about these planets outside our galaxy is mostly theoretical.

The first snapshot of an exoplanet should also be part of the photos that NASA will publish on Tuesday.

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