00:00Bang, or should I say Big Bang, the Big Bang, hmm.
00:07After the Big Bang, the universe looked like a broth of protons, neutrons and electrons.
00:13After starting to cool down, protons and neutrons began to combine,
00:18first forming ionized hydrogen atoms and later helium.
00:22These ionized helium and hydrogen atoms attracted electrons,
00:26transforming them into neutral atoms.
00:28As a result, light was able to move freely for the very first time,
00:32since it was no longer dispersed by free electrons.
00:35What does that mean?
00:37The universe was no longer dark.
00:40However, it took a few hundred million years after the Big Bang
00:46for the first sources of light to begin to appear.
00:49It was at this moment that cosmic darkness really ended.
00:54We do not know for sure what the first light of the universe looked like
00:58or how the first stars were formed.
01:01Fortunately, the James Webb Space Telescope helps us find answers.
01:05How?
01:07Simply because it is an infrared telescope.
01:10Why is it important? Let's try to understand.
01:13Imagine a star.
01:15It is a very, very old star.
01:17Maybe the first.
01:19The light left this star 13.6 billion years ago
01:23and undertook an incredible journey through space and time.
01:26It must reach our telescopes.
01:28When this light reaches us, its color or wavelength turns red.
01:33This is what we call a shift to red.
01:37This shift is due to the fact that, when it comes to very distant objects,
01:41Einstein's Theory of General Relativity comes into play.
01:45According to this theory, the expansion of the universe
01:48also means that the space between objects stretches,
01:51which moves them away from each other.
01:53But that's not all.
01:55Light also stretches,
01:57which moves it to larger wavelengths.
01:59Finally, this light reaches us in the form of infrared.
02:04In other words, the shift to red means that the light emitted at the origin
02:09by the first stars or galaxies in the form of ultraviolet or visible light
02:14is shifted to redder wavelengths
02:17when we see it here and now.
02:22For the most distant objects with a very high shift to red,
02:26this minimum of visible light is displaced in the electromagnetic spectrum
02:30located in the near and medium infrared.
02:33That's why, to see these objects from space,
02:36we need a super-powerful telescope.
02:38The Webb telescope can see up to 100 million or 250 million years after the Big Bang.
02:43Which is incredibly impressive.
02:46By observing the universe in infrared,
02:49the James Webb telescope allows us to see things
02:52that no other telescope has ever shown us before.
02:55The main objective of this incredible device
02:58is to study the formation of galaxies and stars
03:01that appeared in the first moments of the universe.
03:04To go back so far in time,
03:06you have to look further into space.
03:10All this because it takes time for light to travel to us.
03:14As a result, the further we look, the further we go back in time.
03:19To find the first galaxies,
03:21James Webb will make an ultra-deep survey of the universe in the near infrared.
03:26He will then continue with other research methods.
03:30As you remember, at the beginning of the universe,
03:33the gas between the stars and galaxies was opaque
03:36and the energetic light of the stars could not penetrate it.
03:40Then, about a billion years after the Big Bang,
03:43it suddenly became completely transparent.
03:46Why?
03:47The James Webb telescope may have found the answer.
03:51At one point, the stars of the first galaxies emitted enough light
03:56to ionize and heat the gas that surrounded them.
03:59This allowed to clear sight for hundreds of millions of years.
04:03The most recent knowledge of scientists
04:06dates back to a period called the ionization era.
04:10At that time, the universe underwent spectacular changes.
04:15After the Big Bang, the gases of the universe were incredibly hot and dense.
04:20Hundreds of millions of years have passed,
04:23and the gas has cooled.
04:25Then something amazing happened.
04:28It's as if the universe had pressed the repeat button.
04:32The gas has become ionized and hot again.
04:35This phenomenon could be due to the formation of the first stars.
04:39Then, millions of years later,
04:42this mixture has become transparent.
04:45For a long time, researchers have hoped to find concrete proof of these changes.
04:50Today, the telescope teaches us that these transparent regions
04:53are located around galaxies.
04:55Astronomers have seen these galaxies re-ionize the gas that surrounds them.
05:00Even better, they have managed to measure the size of these transparent regions.
05:05And they are gigantic compared to the galaxies themselves.
05:09Imagine a golf course.
05:11Now imagine a small weight floating inside.
05:15You got it.
05:17And guess what?
05:19These tiny galaxies were at the origin of the entire ionization process,
05:24releasing huge regions of space around them.
05:27These transparent bubbles continued to grow until they merged
05:31and made the entire universe transparent.
05:34The research team chose to target an earlier period at the end of the ionization era.
05:39At that time, the universe was not quite opaque,
05:42but not quite clear either.
05:44It was a patchwork of regions where the gas was in different states.
05:48To discover this amusing fact,
05:50astronomers oriented the James Webb telescope towards a quasar,
05:54an incredibly bright space object.
05:56It acted like a gigantic flashlight,
05:59moving towards us through different gas regions.
06:02Its light was either absorbed by the quasi-opaque areas,
06:05or freely crossed the areas where the gas was transparent.
06:10Scientists then used Webb to examine the galaxies in this region of space.
06:16They discovered that these galaxies were generally surrounded by transparent regions
06:20with a radius of about 2 million light years.
06:24For comparison, the area released by the galaxies
06:27corresponds approximately to the distance separating our galaxy,
06:30the Milky Way, from our closest neighbor, the Andromeda galaxy.
06:35And the telescope was able to observe these galaxies
06:38releasing the space around them.
06:40It was the end of the ionization era.
06:43Until then, no one knew what had caused this process.
06:47The team plans to dive into the research of other galaxies
06:50in five additional areas.
06:53The results obtained by the Webb telescope in the first area
06:56were extremely clear.
06:59While astronomers expected to identify
07:01a few dozen galaxies existing at the time of the reionization,
07:06they found 117.
07:10Let's now talk a little about the main hero of today's video,
07:13the James Webb Space Telescope.
07:16It is an absolutely amazing instrument,
07:19100 times more powerful than the Hubble Space Telescope.
07:22And it has observed places
07:24located at 13.4 billion light years.
07:29To say that the James Webb Space Telescope is a bit expensive
07:31is an euphemism.
07:33While originally, the cost of the telescope was estimated
07:35between 1 and 3.5 billion dollars,
07:39the entire development process cost about 10 billion dollars.
07:43For comparison, the construction and launch of the Hubble Space Telescope
07:47cost NASA 4.7 billion dollars.
07:51And it took another 1 billion dollars to put it into orbit.
07:56Although the James Webb Space Telescope is three-story high
07:59and as large as a tennis court,
08:01its mirrors are the lightest telescope mirrors of all time.
08:05During the manufacturing process,
08:07their weight was reduced by 92%.
08:12When you look at them,
08:13the telescope mirrors seem to be made of gold.
08:17In reality, they are made of beryllium.
08:19It is a steel, light and fragile gray metal.
08:23A layer of gold is applied on each mirror, it is true.
08:26But they cannot be made entirely of gold,
08:29because this precious material tends to dilate and contract,
08:33even in case of low temperature variations.
08:37Thus, the total amount of gold contained in the James Webb Space Telescope
08:42is less than 60 grams,
08:44or a piece of gold the size of a golf ball.
08:47And the gold plates that cover the mirror
08:49have a thickness of less than 1000 atoms.
08:52As far as the telescope's capabilities are concerned,
08:54it would be able to clearly see an American penny
08:57at a distance of 38 km
08:59and a football ball at a distance of 547 km.
09:04The James Webb Space Telescope side cools by itself
09:07and its temperature does not exceed minus 223 degrees Celsius.
09:12It is quite cold to make liquid nitrogen.
09:15A huge five-layer solar shield surrounds the telescope
09:18and reflects the sunlight as much as possible,
09:21allowing the telescope to remain cold.
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