Les scientifiques ont découvert quelque chose d'incroyable — le "cœur ancien" de la Voie lactée ! C'est un groupe d'environ 18 000 étoiles qui sont parmi les plus anciennes de notre galaxie, datant de plus de 12 milliards d'années. Ces étoiles se sont formées lorsque l'univers était jeune et que la Voie lactée commençait juste à prendre forme. Elles sont situées profondément au centre de la galaxie, dans une région que les astronomes avaient du mal à étudier à cause de toute la poussière et les gaz sur le chemin. Grâce à des télescopes avancés et des outils spéciaux, les scientifiques ont pu percer à travers le désordre cosmique et découvrir ces étoiles, nous offrant un aperçu des premiers jours de la Voie lactée. Animation créée par Sympa.
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FunTranscript
00:00Ah, hang on to your long view, space rat.
00:04The scientists have made an amazing discovery.
00:07They discovered the ancient heart of our galaxy, the Milky Way.
00:11But what is this ancient heart, and what does it tell us about the history of our galaxy?
00:16Let's see it together.
00:17Is that all?
00:18Yes, yes. Thank you, Captain Jack.
00:20At your service.
00:21Ah!
00:22And yes, what do you want?
00:23He's a space pirate.
00:25The Milky Way is not just a chocolate bar.
00:28It is above all a majestic spiral galaxy that houses billions of stars, planets and other celestial objects.
00:34And it extends over an impressive distance of about 100,000 light-years.
00:39The Milky Way has a characteristic shape, with a central bulb from which spiral arms start.
00:45These arms, comparable to space suburbs, are areas where the stars are more dispersed and the neighborhood more peaceful.
00:52Constituted of gas, dust and stars, they move in harmony, forming a circular pattern around the galactic center.
01:00Among these spiral arms are huge expanses of interstellar space.
01:05These regions, although essentially empty, are home to fine nebulae of gas and dust, as well as captivating spectacles,
01:13such as vast areas of star formation or nebulae with brilliant colors.
01:19The Milky Way is also surrounded by a vast halo of black matter,
01:23a mysterious and invisible substance whose gravitational effects we only perceive.
01:28This halo plays an essential role in maintaining the cohesion of the galaxy and spreading far beyond the visible regions.
01:35And finally, here is the center of the Milky Way, where an intense activity is concentrated.
01:41We find a supermassive black hole, whose mass is about 4 million times greater than that of our sun, Sagittarius A.
01:49This black hole generates phenomena among the most energetic in the galaxy, such as the emission of powerful energy jets.
01:56You probably remember the first picture of a black hole to have gone around the web?
02:01It was Sagittarius A that we managed to immortalize thanks to its proximity to Earth.
02:07All in all, the center of the Milky Way is full of closely clustered stars, forming a particularly dense cluster.
02:14This is precisely where astronomers have recently made an extraordinary discovery.
02:19The heart of our galaxy has been identified.
02:22And what a heart! It is a real fossil.
02:25And a little respect for the elders.
02:28A team of scientific emirates has created a cluster of 18,000 stars, which appeared shortly after the Big Bang.
02:34These ancient stars constituted the primitive nucleus of the Milky Way.
02:38They date from a time when our galaxy was only a collection of proto-galaxies,
02:42uniting progressively to give birth to a larger and more complex structure.
02:47Researchers have nicknamed this cluster the poor old heart of the Milky Way.
02:52Incredible, isn't it?
02:54These stars, over 12.5 billion years old, may only represent 0.2% of the total mass of our galaxy.
03:03But their importance is inestimable.
03:06They constitute the founding bricks that shaped the nucleus around which all the other stars and planets took shape.
03:13But how did these stars become the heart of the galaxy?
03:16How were they formed?
03:18And how did we discover them?
03:20To answer these questions, we must go back in time, to an infinitely distant past.
03:27It was once, nearly 14 billion years ago, the Big Bang.
03:31It was at this moment that our universe was born.
03:34In its first moments, it was of an unimaginable heat.
03:38Then, by cooling down little by little, small pockets of gas began to regroup under the effect of gravity, giving birth to the first galaxies.
03:47The Milky Way is one of these galaxies.
03:49It also began in the form of a modest concentration of gas and dust.
03:55Then, over time, it began to structure.
03:59The first stars, called proto-stars, appeared within the clouds, and their gravity attracted more matter.
04:06This process, spanning millions of years, finally gave birth to the Milky Way.
04:12But to explore more deeply the history of our galaxy, it is necessary to locate these proto-stars, a task that is complex.
04:21It is by analyzing the data from the Gaia mission of the European Space Agency, using a neural network, that researchers were able to identify this ancient core.
04:30The Gaia telescope, a space observatory launched in 2013 by the European Space Agency,
04:36has the mission to map the position and movements of more than one billion stars within our galaxy.
04:42One billion stars!
04:44A colossal task, comparable to counting each grain of sand on a beach.
04:49But Gaia is perfectly up to this challenge.
04:52And how does it work?
04:54The telescope is equipped with two sophisticated cameras that simultaneously photograph the sky.
04:59Their power is such that they can detect stars a million times less luminous than those visible to the naked eye.
05:06By taking multiple clichés of each star, Gaia allows us to follow their movements with remarkable precision.
05:14The data collected by Gaia gives astronomers a better understanding of the structure and history of the Milky Way.
05:21It reveals unprecedented information about stars, such as their age, temperature or chemical composition.
05:28In addition, Gaia contributes to the research of exoplanets, these bodies that gravitate around stars located outside our solar system.
05:37As part of this research, astronomers used Gaia and the most precise 3D map of the Milky Way ever made.
05:45To identify the primordial group, they had to analyze nearly two million stars.
05:50One of the methods to estimate the age of stars is to observe their luminosity and temperature,
05:56thus studying a short phase of their evolution, known as a sub-giant.
06:02But imagine to see located, within the immense center of the Milky Way, a tiny group of stars over 12.5 billion years old.
06:10It's like looking for a needle in a haystack.
06:13Fortunately, researchers had a size advantage, metals.
06:18In the primitive universe, the cores of the first stars were so hot and dense that they were able to fuse atoms,
06:25giving birth to heavier elements, called astronomy metals.
06:30However, these metals do not necessarily correspond to the materials we call in everyday life.
06:37The more massive a star is, the more it produces metals during its existence.
06:42When the first stars reached the end of their lives, they exploded by dispersing these metals.
06:48These then mingled with the surrounding gas and contributed to the formation of the next generations of stars.
06:54Over time, as the universe aged, new generations of stars followed, each containing more metals than the previous one.
07:03Do you see where this is going?
07:05The older a star is, the less it contains metals.
07:09This meant that it was time to turn to a real galactic archeology.
07:13The team formed the IA to identify the oldest and richest stars in metals.
07:20And it took up the challenge.
07:22It spotted a huge pile of stars, all located less than 30,000 light-years from the center of the Milky Way.
07:29Then, astronomers distinguished the stars that made up the ancient core of those from a dwarf galaxy.
07:36In the end, only the original stars around which the Milky Way had grown remained.
07:42This discovery is truly fascinating.
07:44It highlights the remains of the first stages of the history of the Milky Way.
07:48The simulations of its formation proved to be of great precision.
07:52The old stars were exactly where they had been predicted.
07:56Imagine, stars that remember the universe from its beginnings are still today at the heart of our galaxy.
08:04Isn't it extraordinary?
08:06But why is it so important?
08:08By studying these stars, scientists have made remarkable discoveries.
08:12They have confirmed that the core of the Milky Way was initially stationary, and only began to rotate as it grew.
08:19This means that the Milky Way was formed thanks to the fusion of 3 or 4 proto-galaxies,
08:24these stars constituting its very first core.
08:27But even after billions of years and numerous fusions, the heart of the Milky Way has remained intact.
08:33Like an oasis protected within the cosmic tumult.
08:37The Milky Way is a vast and complex structure, full of mysteries and wonders yet to be discovered.
08:44It is a true splendor of the universe, and we have the chance to inhabit it.
08:48But exploration does not stop there.
08:50Researchers want to learn more and more about the formation of our galaxy,
08:54and plan to study these ancient stars with increased precision.
08:59Who knows what revelations could emerge?
09:01Perhaps they will discover the types of supernovae responsible for the elements we know today.