Le télescope spatial James Webb de la NASA vient de découvrir six galaxies qui défient totalement ce que nous pensions savoir sur l'univers! Ces galaxies sont bien plus grandes et plus matures qu'elles ne le devraient, compte tenu de leur âge. C'est comme trouver des arbres entièrement développés dans un jardin que vous avez planté la semaine dernière. Les scientifiques se grattent la tête en essayant de comprendre comment ces galaxies sont devenues si grandes, si rapidement. C'est un mystère passionnant qui pourrait changer notre compréhension du cosmos! Animation créée par Sympa.
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FunTranscript
00:00They should not have existed. No one expected to discover them.
00:05Scientists fail to explain their formation.
00:08And yet, it did not prevent the James Webb Space Telescope from identifying them.
00:17These six galaxies, as massive as our Milky Way, are populated with mature red stars.
00:23They are so far from us that they appear as tiny red dots.
00:29Even for this high-end telescope.
00:31Astronomers have analyzed the light emanating from these galaxies and estimated their age.
00:36They would have appeared 500 to 700 million years after the Big Bang.
00:43So far, nothing surprising.
00:45Galaxies so young are not really rare.
00:48Scientists think that the first clusters of stars could emerge shortly after the universe left what is called the Dark Age.
00:59Which corresponds to the first 400 million years of its existence.
01:02At that time, only a thick fog of hydrogen atoms filled the cosmos.
01:09What is particularly strange about these galaxies is their unmeasured size and the advanced age of the stars that make them up.
01:16This contradicts current theories about the appearance and evolution of the universe in its early years.
01:22In addition, these observations differ from those made previously by the Hubble Space Telescope, the less advanced predecessor of James Webb.
01:33So, according to scientists, what are these first galaxies supposed to look like?
01:38The answer is simple, young and small.
01:41Indeed, until now, most of the galaxies of the primitive universe discovered are babies of space, small and blue.
01:49They seemed to have emerged only recently from the primordial cosmic soup and were still forming their first stars and other ensembles.
01:57Most of the young stars are actually blue.
02:00As they age, they acquire a more reddish hue after having burned their stellar fuel and cooled down.
02:06This is why astronomers did not expect to discover red, aging stars in ancient galaxies that the James Webb telescope was designed to observe.
02:17Another unexpected surprise would have been to discover galaxies more massive than a billion suns.
02:23And yet, this is indeed what happened.
02:27The recently discovered galaxies are almost as immense as the Milky Way, with respective masses only 2 to 4 times less.
02:35The most surprising thing is that these galaxies were already so vast when the universe had only reached 3% of its current age.
02:43But before astronomers revise their theories to explain how galaxies so immense could form so quickly after the Big Bang,
02:52it is crucial to verify that these observations are not due to another space phenomenon.
02:58Even in this specific case, most alternative theories require the introduction of entirely new concepts.
03:05One of these theories proposes that stars in the primitive universe emit light in an unusual way.
03:12Since astronomers were not aware of this, this possibility was not included in their model.
03:18Or, what we know about the formation of stars could be inapplicable to the primitive universe.
03:25If one of these theories turned out to be accurate, it would completely revolutionize our understanding of stellar formation.
03:35Now let's move on to the device that allowed astronomers to discover these extraordinary galaxies.
03:41The James Webb Space Telescope is a technological marvel about 100 times more powerful than the Hubble Space Telescope.
03:48And Hubble, in its time, was able to observe objects located 13.4 billion light years away.
03:56The James Webb Space Telescope is also very expensive, and it is an euphemism.
04:01Although its initial cost was estimated at between $1 and $3.5 billion,
04:06the complete development will ultimately have cost the bagatelle $10 billion.
04:10In comparison, the construction and launch of the Hubble Space Telescope, with Eve, cost $4.7 billion at NASA,
04:18with Inve, $1.1 billion more required to repair it in orbit.
04:24Although the James Webb Space Telescope is the height of a three-story building and the size of a tennis court,
04:30these mirrors are the lightest among all the great telescopes ever built.
04:35When they were designed, their weight was reduced by 92%.
04:43At first glance, the mirrors of the telescope seem to be made of gold.
04:47But they are actually made of beryllium, a light metal.
04:51Although a gold coating is applied to each mirror, they cannot be entirely made of it,
04:57because this precious material expands and contracts with temperature variations.
05:05In fact, the total amount of gold used in the James Webb Space Telescope is less than 57 grams,
05:11which represents a piece of gold the size of a golf ball.
05:15The layers of gold covering the mirrors are only 1,000 atoms thick.
05:20As for the telescope's capacity, it can clearly distinguish a 1-centimeter piece at a distance of 38 kilometers
05:27and a 550-kilometer football ball.
05:35The James Webb Space Telescope side maintains an exceptionally low temperature.
05:41The James Webb Space Telescope side maintains a temperature not exceeding 223 degrees Celsius,
05:48in other words, cold enough to liquefy nitrogen.
05:52A giant five-layer solar shield surrounds the telescope and reflects the solar light,
05:58thus keeping the device at a low temperature.
06:04It is thought that James Webb will be able to detect water on distant exoplanets.
06:08For a long time, astronomers have been discovering new planets orbiting around their own stars,
06:13observing the slight variations in luminosity that occur when planets pass in front of their stars.
06:19In addition, it is possible to analyze the spectral signature of light to determine the chemical composition of a planet.
06:27The strongest and most readable signatures appear in the infrared spectrum.
06:33And guess what?
06:35The James Webb Space Telescope is equipped with high-tech infrared instruments.
06:39These can help scientists discover new planets and even identify the presence of water on them.
06:47The telescope was launched near the equator because the Earth's rotation there is slightly faster,
06:52thus giving an additional impulse to the rocket.
06:55Once the James Webb Space Telescope runs out of fuel,
06:59it will continue to gravitate around the Sun indefinitely.
07:02Although the device was not designed to be maintained or improved,
07:06it could potentially be refueled by robots, which would extend its lifespan.
07:13At first, astronomers at CITESOMF were convinced that it would take time for James Webb to discover anything exciting.
07:19They thought that the first galaxies to be observed would be so dark and small
07:24that the telescope would only discover a few rare distant candidates.
07:29However, the results exceeded all expectations.
07:32As soon as the first images were broadcast, scientists began to discover countless galaxies,
07:38vast, bright, and remarkably old.
07:41The competition between research groups to identify new clusters beating all records still persists today.
07:49An astronomer even claimed that the scientific community was on edge
07:53because no one had really anticipated such spectacular results.
07:58One of the main objectives of the Webb Space Telescope
08:01is to observe the light of the very first stars and galaxies in the universe.
08:05Alas, the farther an object is, the faster it moves away from us,
08:10and the more the light it emits must travel from a distance,
08:13thus stretching towards the infrared of the spectrum,
08:16a phenomenon known under the name of redshift in astronomy.
08:20However, thanks to its high-end infrared instruments,
08:24James Webb can reveal worlds that were previously invisible.
08:28Thanks to this telescope, we were able to observe incredibly distant galaxies,
08:33formed about 13.8 billion years ago.
08:37This means that the light detected by James Webb took more than 13 billion years to reach Earth.
08:43Can you imagine what that means?
08:46Among these galaxies, one stands out particularly.
08:49It seems to be the oldest ever discovered by astronomers.
08:54It is called Galas Zezam 13 and dates back only 300 million years after the Big Bang.
09:01The oldest galaxy previously identified by scientists, GN Zaonze,
09:07was discovered by the Hubble Space Telescope and dates back 400 million years after the Big Bang.
09:14During this barely explored period, the very first galaxies and stars began to emerge.
09:22But how exactly did this process take place?
09:25No one knows for sure, at least for now.
09:29This phenomenon could depend on unknown physical laws,
09:32including the influence of dark matter and dark energy,
09:36or on some interactions that have yet to be studied between gas, dust and stellar light.
09:42The fact is that, thanks to Webb telescopes,
09:45scientists can now test their theories on events that occurred after the universe was born.