Il existe un objet bizarre dans l'espace qui n'est ni une étoile ni une planète, mais qui est plus chaud que le Soleil ! On l'appelle une "naine brune", parfois surnommée une "étoile ratée". Les naines brunes sont trop petites pour déclencher la fusion nucléaire comme de véritables étoiles, mais elles sont beaucoup plus grandes et plus chaudes que les planètes ordinaires. Une naine brune, appelée WD 0032-317B, est particulièrement étrange car elle est chauffée par une naine blanche voisine (un cœur résiduel ultra-chaud d'une étoile morte). Cela fait que son atmosphère atteint des températures de plus de 14 000 degrés Fahrenheit, plus chaud que la surface de notre Soleil ! C'est un exemple incroyable de la façon dont l'univers peut être étrange et surprenant. Animation créée par Sympa.
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FunTranscript
00:00It seems that scientists have discovered a strange object in space and they do not know exactly if it is a star or a planet.
00:08What we know is that it is located 1400 light years from us.
00:13Which leads us to wonder about what we thought we knew about the universe.
00:18Let me explain the dilemma.
00:20We can determine if an object is a star or a planet depending on its mass or the amount of matter it contains.
00:28Stars have a large mass, which gives them a strong gravity that compresses them strongly.
00:33This compression creates high temperatures inside.
00:36As a result, they shine with a thousand lights.
00:40Planets have a smaller mass and their gravity is therefore weaker.
00:44They do not undergo the same compression and therefore do not have the high temperatures of stars.
00:49If planets shine, it is because they reflect the light of their stars, as our beautiful Earth does with our sun.
00:56Well, this strangeness is between the two.
00:59We consider that it is a brown dwarf, a particular type of large-sized gas proto-star.
01:06Brown dwarfs generally resemble Jupiter in terms of atmosphere, but they are much larger, with a diameter of 13 to 80 times higher.
01:15If a brown dwarf has a mass more than 80 times higher than that of Jupiter, then it can start to burn hydrogen like any star does.
01:24This is how stars shine in the sky.
01:27But normally, brown dwarfs are not as hot as stars.
01:31Their inability to burn hydrogen has even earned them the nickname of missed star.
01:36They burn at about 2200 ° C, which is colder than most stars.
01:43But this object defies the norm.
01:45Its temperature reaches the incredible bar of 7700 ° C.
01:50Let's put this into perspective.
01:52The hottest day in history was recorded in the Valley of Death, in California, more than 100 years ago, with a temperature of 57 ° C.
02:02The people of the time must have had the impression of melting with everything around them.
02:08Now imagine that you are getting closer to the sun, as if you were traveling to Venus.
02:15Venus can reach the insane temperature of 460 ° C.
02:21But there is not only the distance that matters.
02:24Mercury is the planet closest to the sun.
02:27But it is colder than Venus.
02:30If Venus is so hot, it is because of the greenhouse effect.
02:34Did you know that a long time ago, Venus could have been a place where it was good to live?
02:39Or at least, it could have sheltered forms of life.
02:42But at some point, it began to trap carbon dioxide, and it ended up creating a thick fog that did not let the heat escape.
02:51That's why it's so hard to explore.
02:54The probe that managed to spend the most time on Venus only lasted two hours.
02:59It's still longer than what I can do at work.
03:03After that, I melt.
03:05So yes, you get to the sun.
03:09Its surface burns at an incredible temperature of 5,500 ° C.
03:14And what is fascinating is that this strange brown star we are talking about is even hotter than that.
03:21Of course, it is not hotter than the heart of the sun, whose temperature can reach 15 million ° C.
03:28But it is still very impressive and unusual for a brown dwarf to be so hot.
03:34This is at least what everyone thought, until we realized the reason for this phenomenon.
03:39The brown dwarf is remarkably close to another star, which, it, falls into the category of white dwarfs.
03:46They are so close to each other that our mysterious brunette makes an orbit around her white friend in just two or three hours.
03:54As if we were old there.
03:57As they are very close, they are in a state of gravitational lock, like the moon and the earth.
04:03This means that this brown dwarf always presents only one of its faces to its white dwarf.
04:08The other face is always in the dark.
04:11For this reason, our brown dwarf is overheated only on one side.
04:15It is therefore this illuminated face that confused us,
04:18while the temperature of its nocturnal face corresponds to what we expect from a brown dwarf.
04:23But these extreme conditions will not last long.
04:26Such a high temperature causes the molecules of its atmosphere to disintegrate into individual atoms,
04:32and as these molecules fragment, our brown dwarf slowly disappears.
04:38If you think this brown dwarf is hot, what would you say about Eta Carinae?
04:42It is a star located at about 7,500 light-years from Earth, in the constellation of the Cairn.
04:49It belongs to a category of stars called the blue luminous variables.
04:54An astronomer noticed it for the first time in the 17th century.
04:58But at the time, it was just an ordinary star of average luminosity.
05:02Nearly 200 years later, another astronomer came across it.
05:06But this time, it was a very bright star, one of the brightest in the sky.
05:12A few years later, it reached its highest level of luminosity
05:16during a major event called the Great Eruption.
05:19At that time, the star was easily visible in our night sky.
05:24It released a surprising amount of light,
05:27as important as that emitted during the explosion of a supernova.
05:31And it stayed that way for a few years, which is not the case of exploding stars.
05:36When the event reached its peak, it decided it was time to say goodbye.
05:41But it still hesitates a little, which means it is still alive, but it is less luminous than before.
05:48There is also a nebula around Eta Carinae.
05:52It is a gas and dust shell that formed during the Great Eruption.
05:56It even blocked part of the star's light.
05:59Eta Carinae is a binary stellar system.
06:03In other words, two stars orbit each other.
06:07One of them has a temperature of about 14,700°C,
06:11the other of 34,650°C.
06:14The main star of the Eta Carinae system, the most massive of the two,
06:18is 100 times heavier than our Sun.
06:21Because of its enormous mass, scientists predict that this star could explode
06:26during a powerful event known as a supernova, but not before several thousand years.
06:31You may have already guessed what is the hottest phenomenon in the universe.
06:35Yes, a supernova.
06:37It is thanks to it that we know that the life of a star is over.
06:41These are the most powerful explosions in space.
06:44They occur when a star is between 8 and 40 times more massive than our Sun.
06:51Its core can no longer produce enough energy
06:54through a process called fusion,
06:57so that the star can no longer withstand its own gravity.
07:01It is therefore a kind of stellar exhaustion.
07:04The star can no longer face such a heavy workload
07:07and its core is let go.
07:09During a supernova, the temperatures at the center of the star
07:12can be 6,000 times higher than in the center of the Sun.
07:16It also happens that a particular type of star, called white dwarf,
07:20suddenly resumes its nuclear fusion and, boom,
07:23you get a supernova again.
07:26Kepler's supernova occurred at the beginning of the 17th century
07:29and was the last really important to be directly observed from Earth.
07:34On average, supernovas in our galaxy occur three times a century.
07:39A supernova of lesser importance occurred in 1987
07:44when a blue supergiant named SN 1987A
07:49exploded in one of the satellite galaxies of our Milky Way,
07:53the Great Magellan Cloud.
07:55This explosion was so powerful that it could be observed with the naked eye,
07:59although it occurred at an incredible distance,
08:02at 168,000 light years from our planet.
08:05What a beautiful day, isn't it?
08:08We can also talk about the hottest thing ever created,
08:12made in an amazing place, Switzerland.
08:15No, it's not a super hot chocolate.
08:19A group of scientists created a subatomic soup
08:23called quark and gluon plasma.
08:25During this experiment, the temperature became
08:28250,000 times higher than that of the heart of the Sun,
08:31the goal was to recreate the conditions that existed shortly after the Big Bang
08:35when the universe was still in a state of chaos.
08:38Well, let's go even further.
08:40In theory, things can get even hotter.
08:44Have you heard of Planck's temperature?
08:47It is an extremely high temperature,
08:50with numbers that we can't even imagine.
08:53A supernova is a warm tea compared to this madness.
08:56And who knows what the matter does at these temperatures?
08:59That's all for today.
09:01You are back in your comfortable universe.
09:04Bye!