Transcription
There are events that are already written, those of incredible beauty and unparalleled violence that in the near future will unleash in the sky and which we will talk about today are part of them. But before going to see how much it could impact our planet, allow me to thank My Heritage thanks to whom I was able to put names on many of my ancestors and see in just a few weeks my family tree enriched with a dozen branches going back up to five generations. For this, I simply provided some basic information about myself and they then took care of searching through the nearly 33 billion historical records and archives to which they have access. And in a few days, my tree began to come alive, constantly enriching itself with new ramifications like a good series full of twists. And if I did not discover myself to be the heir, forgotten, of a castle in Spain, I found there much more than treasures buried by pirates. Because the time machine and going back in time and My Heritage allowed me to get my hands on the shadows of enigmatic and endearing characters. Who was this Jean Vaillant who recently appeared in my tree? born in 1709, a peasant like nearly 95% of the French population of his time and yet 100% fascinating and to whom I indirectly owe my life. With my grandmother, we spent hours imagining the existences of these characters who are part of the family's past. A highwayman or a thwarted adventurer who spent his whole life in the same valley. In addition, on My Heritage, you can even have fun recoloring old black and white photos, like here, that of my grandfather when he was a child. In short, to easily dive into the mysteries of your origins and try My Heritage for free for 14 days, simply use the link I put in the description or the QR code displayed on the screen. Amusingly, if we could go back far enough in time, we would end up encountering humans, whether they were your ancestors or mine, who witnessed the phenomenon we are about to discuss. In the year 100, a star of unparalleled brightness suddenly appeared in the sky. 100 times brighter than Venus, it cast marked shadows on the earth at night and at its peak was even visible in broad daylight. Then its brightness gradually declined and after 2 years, it had completely disappeared. The astronomers of the time thought they were witnessing the birth of a new star. It was in reality its death, the sign of the end. This is not fiction. It has already happened and it will happen again because in the cosmos there are giant stars or unstable pairs of stars that inevitably end their lives in a cataclysmic explosion called a supernova and emit in a few days as much energy as billions of suns combined. Over the last millennium, the appearance of these powerful ephemeral stars can be counted on the fingers of one hand. We observed one in the year 100, in 1054, in 1572, and in 1604. And each time, when we point our telescopes to where these celestial bodies momentarily appeared, we can see the remnants of vanished stars, whose burning and expanding remains are still clearly visible centuries after the explosion took place. On a cosmic scale, these events are rare. It is estimated that on average two to three supernovae explode per century. in our galaxy, space is vast and most of the time, these monsters of space are for us nothing more than a powerful and new ephemeral light that for a few weeks illuminates a distant constellation before disappearing. All the supernovae we have identified with the naked eye in recent centuries exploded thousands of light-years away and had no consequences for our planet. But it has happened in the past that these explosions occurred much closer, so close that their effects were not simply visible but literally terrible. It is thought that 2.6 million years ago, a supernova exploded 30 times closer to us than the one observed in the year 100. And this proximity had great consequences. The story always begins the same way. A new star appears in the sky. Abnormally bright, it quickly gains power until it becomes as luminous as the full moon, practically eclipsing the entire firmament. Soon, it becomes almost day in the middle of the night and during the day, the star is still there. For a few months in the sky, there is like a second little sun. Except that this time, the proximity of the dying star, much more marked and more powerful than the previous ones, will wreak havoc. Its light coming from the depths of space carries destruction with it. Because in the wake of its explosion, bursts of high-energy particles were projected in all directions like waves on the surface of a furious cosmic ocean. And after spending more than a century traveling silently through interstellar space at the speed of light, part of the supernova's energy strikes our planet in the form of a deluge of gamma radiation and cosmic rays which, by relentlessly penetrating the upper atmosphere, will generate a rain of secondary energetic particles triggering a series of planetary-scale upheavals. At an altitude of a few tens of kilometers, the ozone layer is attacked and a large part of this protective shield is destroyed, leaving the Earth's surface vulnerable to the most aggressive solar radiation and cosmic rays. For all living beings evolving on the surface, the light of our star becomes a threat. On land, plants die in series and in the oceans, marine organisms evolving in the layers near the surface such as phytoplankton perish. In a few months, the collapse of the first links in the food chain leads to that of a large part of the biosphere. To this carnage, the supernova, in its wake, adds a general climate upheaval. Because by impacting the molecules of our atmosphere, the cosmic rays have triggered a cascade of chemical reactions and created large quantities of nitrogen oxides which will gradually form a vast cloud cover covering the planet with a strange opaque and hazy veil. In a few years, the sunlight reaching the ground drops dramatically, and so does the global temperature. A planetary-scale nuclear winter sets in. As crazy as it may seem, this scenario of mass extinction and climate upheaval caused by a supernova explosion is considered very credible. Because the global cooling is brutal. The beginning of the Pleistocene, which saw the average temperatures of our planet drop by nearly 5°C, begins around the same time as the impacts of the most powerful of the last clearly identified supernovae are dated. Indeed, in sediments dating from that period, we find large quantities of a strange element, iron 60. A radioactive isotope of iron to which, let's be honest, almost no one attaches importance. But if you are a nuclear physicist, it is one of your favorite atoms. because iron 60 can only come from elsewhere in the cosmos since it only forms under the hellish conditions prevailing in the heart of exploding stars. Its presence found in sediments at the bottom of the Pacific Ocean, in the Antarctic ice, and in lunar rocks is a testimony, a message engraved in stone, telling us that in the past the Earth was indeed struck by radioactive dust propelled into space by the explosion of a dying star. And if you add to this the fact that at the time these particles were deposited, 2.6 million years ago, nearly a third of marine megafauna in the surface layers disappeared, while animals evolving deeper in the oceans were for the most part spared as if they had been protected from cosmic rays by the thickness of the water, you begin to ask yourself some questions. We have also found indirect traces of these past explosions in our galactic neighborhood. Indeed, when we study with our telescopes the amount of matter found between stars, we observe that within hundreds of light-years around, it is 1000 times weaker than its average value in the interstellar medium. In fact, our planet is currently evolving in a relatively empty region of space called the Local Bubble. Today, we believe that this low-density bubble was somehow carved out by the explosion of several supernovae whose blasts and shock waves would have pushed away, blown away, a large part of the interstellar matter it originally contained. We believe we have identified no less than three supernovae that occurred in our galactic neighborhood over the last 10 million years. And by studying the concentrations of iron 60 found in sediments, we were able to estimate that the one from 2.6 million years ago must have exploded about 150 light-years from our planet. This is an absolutely staggering distance that the fastest probes we have sent into space so far would take nearly 3 million years to cover. Another way to represent this is to say that it is 37 times farther than the closest star to us. The fact that an explosion is capable of leaving its mark on fossils and rocks and influencing the climate of a planet located 150 light-years away gives you an idea of its power. Moreover, it is thought that if this supernova had been even five times closer, things on Earth would have, let's say, turned out very badly. To convince ourselves, let's play a little game. Knowing the colossal amounts of energy released by supernova explosions, we can try to see from what distance these explosions are relatively harmless and what is the size of their death sphere, the distance from which they are inevitably fatal. Let's start by imagining that a supernova explodes one light-year away from here. In that case, clearly all the lights are scarlet red. Death would arrive in the wake of a blinding light, filling almost the entire sky and eclipsing the sun in an insidious and silent form. That of an uninterrupted flow of gamma rays and extremely energetic cosmic radiation that would pierce like invisible arrows traveling at the speed of light absolutely all living beings on the surface of the earth. In fact, at one light-year from the explosion, even if we took refuge deep in a nuclear shelter to escape the intensity of the radiation, we would have absolutely no chance of survival. Firstly, because these high-energy cosmic particles would strip the atmosphere entirely, and secondly, because we would be within the range of the explosion's kinetic energy. In other words, entire chunks of matter torn from the star would, in the weeks and months following the arrival of the rays, strike our planet at a fraction of the speed of light, melting its surface. Let's take a step back. At 5 light-years from the explosion, which is roughly the distance of the closest star to us today. It still smells terribly bad because the ozone layer would be literally annihilated by the power of the radiation, and in just a few hours, the Earth would completely lose its natural shield against cosmic and solar radiation. The consequences would be immediate and tragic. The ultraviolet rays of the sun, as well as those from the supernova, would scorch the surface of our planet. Let's go back even further, even at 10 light-years away, and although the explosion's energy has considerably diluted in space, the consequences would still be catastrophic. Overall, the atmosphere should be able to withstand the passage of gamma rays and clusters of atomic particles which, projected at speeds close to that of light, still possess as much energy as a rifle bullet. But even at such distances, and once this extremely powerful radiation has passed, the worst is yet to come because the shock front of the explosion continues its progression in space. And hundreds of years after the sky suddenly lit up, the expanding remnants of the supernova, rich in heavy radioactive elements forged during the explosion, will inevitably end up reaching our planet and depositing there in the form of a rain of atoms, causing deadly long-term genetic mutations. If you doubt the ability of a supernova to eject matter at such great distances, the Crab Nebula should change your mind. These streams of stellar matter you are looking at were ejected nearly 1000 years ago by the explosion of a supernova, that of 1054, and today spread over 11 light-years wide. This is nearly three times the distance separating us from the closest star, and a millennium after the star exploded, the shock wave is still expanding into the surrounding space. Even being 20 light-years away from the explosion, it is thought that 50% of the ozone layer would be entirely destroyed, and all forms of life evolving on the surface literally wiped off the map. Thus, the explosion of a supernova essentially draws a virtual bubble, a death sphere of at least 40 light-years in diameter around it, within which the fury of the explosion is simply unbearable for life evolving on the surface. It is thought that from 30 to 50 light-years from the epicenter, the star's power is sufficiently diluted in space for us to completely exit the death sphere. Beyond this minimum safety distance, things still obviously shake. Atomic nuclei still impact the Earth in large numbers at nearly 10,000 km per year, leaving red-hot marks, iron 60. But overall, the radioactive fallout remains bearable, and all the danger indicators have decreased enough for the blows to be absorbed. So, I imagine a question is burning on your lips. Are we in danger? Are there giant stars around us about to explode and close enough to kill us? Within a radius of 1000 light-years around the Earth, there are 24 stars that will end their lives as supernovae, and a number of them are expected to explode in the near future. By near future, we mean here a few tens to hundreds of thousands of years. Perhaps some have already exploded, and the burst of light produced by their death is on its way to us as I speak these words. Well, said like that, it sounds rather bad for us, but rest assured, the red supergiant Betelgeuse, which is certainly very close to the end of its life, is for example 640 light-years from Earth. The equally massive and threatening Antares is about 550 light-years away. In fact, the closest of these stars likely to turn into a supernova is currently 240 light-years from us. In short, all these potentially threatening stars are currently too far away to be anything other than an unparalleled spectacle of matter and light eruption. And if one of them exploded today, it would only roughly brand our memories. But don't rejoice too quickly. Already, all these stars are moving in the galaxy, and these incessant movements in the sky can just as easily move a potential danger away as bring it closer. We estimate that on average, a star approaches within one light-year of Earth every 500,000 years. And nothing tells us that in the future, the drift of these stars will not end up dangerously bringing one closer at the precise moment it explodes. And above all, we believe we have discovered two types of giant stars capable of extending the size of the death sphere to absolutely terrifying proportions. The first of them has the particularity of having expelled a large part of its outer layers into space even before exploding. And hundreds of years after being ejected from the star, when this drifting matter cocoon is caught up by the ejections from the explosion, it becomes terribly radioactive and begins to emit in all directions. large quantities of X-rays which for thousands of years will be capable of stripping the protective layers of the upper atmosphere of planets located up to 150 light-years away. As for the second type of star that is very likely to displease you, they are Hypernovae. A type of supernova on steroids, and whose explosion, 10 times more powerful than an ordinary supernova, has the particularity of concentrating the vast majority of the energy released into two emission beams that extend the range of danger to nearly 10,000 light-years away. In fact, these kinds of death rays produced by Hypernovae, called Saama, have such an energy density that we are able to detect those that come to us from explosions that occurred at the edge of the observable universe. Even being 1000 light-years away from the Hypernova, being swept by the three beams of a gamma-ray burst is certain death. And up to ten light-years away, it is the assurance of a deep bite into the atmosphere. And I imagine you will be happy to learn that in our galactic neighborhood there are a number of giant stars capable of creating such cataclysms, such as the gigantic and already partially torn Eta Carinae, located about 7500 light-years from Earth and on the scale of cosmic time in the last moments of its life, or the terribly unstable WR104 whose tremors and fits of anger foreshadow a cataclysmic end whose theater takes place about 8000 light-years from us and which could well, at the moment of its death, give birth to one of these beams that can contain more energy than our sun will emit in its entire existence. So much so that it is thought that being in the line of fire of such a beam for even 10 seconds can be enough to destroy a part of the ozone layer and lead to a new mass extinction. Gamma-ray bursts being very narrow and supernovae extremely rare to the point that it is estimated that a star of this type explodes once every millions of years on average in a galaxy like ours. We are tempted to say that it would take real bad luck to be hit by one. And where it's comical is that it's entirely possible that in this game, we've already lost in the past. Because the hypothesis of a gamma-ray burst is seriously considered to partially explain one of the most terrible mass extinctions our planet has known in its long history: the Late Ordovician mass extinction, during which, 440 million years ago, 85% of species disappeared. It is statistically estimated that our planet must find itself, on average once every billion years, directly in the line of fire of one of these beams. That leaves a 50% chance of being hit in the next 500 million years. Atmosphere and cold sweats. Anyway, what's the point of worrying? Life began on Earth more than 4 billion years ago, and the fact that it is still here should generally reassure us. Each time resilient, it has managed to start over and reinvent itself. And above all, these energetic rays traveling at almost the speed of light, by the time the message arrives, it is always too late. Perhaps one day we will look up at the sky and witness the appearance of a new star. Fascinated by this light of incredible beauty and violence, like a rabbit caught in the headlights of a 38-ton truck. We will stand there, frozen, staring at the birth of a second sun without realizing that this spectacle is that of the last dance of a star taking its bow, and that this light is that of death on its way. Ultimately, each time, it is the distance to the point of explosion that will determine whether this dazzling spectacle will or will not be the last thing we see. In the heart of these explosions, there is a kind of implacable logic, that of a universe in perpetual transformation where destruction is only the other face of creation. It is ironically thought that it was the shock wave of a supernova that, 4.6 billion years ago, initiated the gravitational collapse of the immense cloud of gas and dust that gave birth to our solar system. In this sense, without these explosions, the sun, the Earth, and everything on them would not be here. And in doing so, we are indirectly the distant heirs of these brutal changes. Children of the cosmos and of star death, which can come to reshuffle the cards and turn the table. 4.6 billion years later, Australopithecines, our distant ancestors, had to face the upheaval caused by another supernova, which perhaps modified climatic conditions, forcing species to adapt and evolve. Thus, paradoxically, this cosmic catastrophe may have laid the foundations for our own existence by contributing to the emergence of humanity as we know it. If you want to have fun thinking about the influences that certain stars could have on us, abandon astrology and embrace astronomy. I'm pasting the link here to the episode that describes in detail the phenomena behind supernovae. Remember to activate the bell and subscribe, because in a future episode, we will see that these deadly phenomena are also, and counter-intuitively, absolutely necessary for the appearance of life. Because these giant stars are true cosmic forges whose explosions disperse into space. dust and ashes that serve as basic elements for igniting other stars, building planets, and even living beings. And don't forget that by using the QR code displayed on the screen, and thanks to the link I put in the description, you can try My Heritage for free for 14 days.