Dear readers, faithful companions of the flashlight and basketball: First of all, I must apologize for a long silence. If you haven’t read anything of mine for several weeks, it’s neither because of laziness nor because of forgetfulness. It is because he was obliged to duties that, although less poetic than the stars, are no less demanding. I was teaching in Zurich and serving on thesis defense panels of young PhD students in physics. These commands return periodically, like the tides, and then you have to immerse yourself in equations, listen, correct, encourage. The little time I had left I gave to my family: to Jocelyne, to the children, to the house at the edge of the forest, to Gino, to Tsigane and Safira. Because there are loyalties that come before galaxies. And then there’s the other uniform. Because I am also a captain and helicopter pilot in the Swiss military. This role requires an annual refresher course and a minimum of fifty hours of flight training, which I must complete each year, however long the stars require of me. Up there, in the cockpit, I am no longer the astronomer who contemplates the sky, but rather the one who travels through it. And believe me, experience is complementary: one teaches patience, the other precision. My little angel: WendyPrivée photo But let’s return to you, dear readers, and above all to America. Because Jocelyne, my lovely Jocelyne, is horrified. She said it with that calm frankness that characterizes her: she is repelled by her president’s cowardice. According to the news, he has just destroyed what little credibility his beautiful country had left. She pities you, honestly. He pities the Americans of good faith who helplessly endure the spectacle of their own decline. And he wishes, with all his heart, that true Americans (those who still believe in democracy, science and dignity) can succeed in countering this cruel criminal. She says it with the tenderness of a distant friend, from our little Switzerland, who knows what it costs to defend one’s own freedom. With that said, dear readers, let’s return to heaven. Because that’s really what I want to talk to you about tonight. We have explored the nebulae, the distant galaxies, the Milky Way, Andromeda, the Sombrero. But there are two galaxies that we have never visited and that are, in a sense, our closest neighbors. Two galaxies visible to the naked eye from the southern hemisphere, two clouds of light perched on the velvet of the southern night. Two galaxies called the Magellanic Clouds, and they are dying, slowly devoured by the Milky Way. 1. Two clouds in the southern sky First you have to imagine the sky of the southern hemisphere, the one seen from Chile, from Australia, from South Africa. A sky that I know well from having spent so many nights in Paranal, on the Hill, contemplating the Milky Way. And there, in that sky, are two milky spots, two luminous clouds that are not clouds at all, but galaxies. The Large Magellanic Cloud, the largest, and the Small Magellanic Cloud, more modest. They are visible to the naked eye, without an instrument, like fragments detached from the Milky Way. Portuguese sailors used them as reference points for navigation, before Magellan, on his trip around the world, made them known in Europe, hence their name. Les Nuages de MagellanESO.org The Large Magellanic Cloud is located about 160,000 light years from us, and the Small Magellanic Cloud is about 200,000. They are the closest galaxies to ours, along with the Sagittarius Dwarf. But their proximity is deceptive: They orbit the Milky Way, captured by its gravity, and are being warped, stretched, torn by the tidal forces of our giant. They have already started to die. 2. The Tarantula: a monstrous nursery The Large Magellanic Cloud houses an object that, in itself, is worth a trip. This is the Tarantula Nebula, the largest known star-forming region in the entire Local Group. It extends across almost 1,000 light years and is so bright that it illuminates the entire Cloud. It gets its name from its filaments of gas and dust, which resemble the legs of a giant spider. Hundreds of thousands of young, massive and fiery stars are being born inside. It is a stellar factory, a cosmic oven, a natural laboratory to understand how stars are born. The Tarantula is so luminous that, if it were at the distance of the Orion Nebula, it would light up Earth’s night sky like a full Moon. It houses R136, a star cluster so young and massive that it surpasses anything we know in the Milky Way. Some of them are more than a hundred times more massive than the Sun and will only live a few million years before exploding as supernovae. The Tarantula is a factory of stars and stellar deaths. The Tarentula ESO, ALMA (ESO/NAOJ/NRAO)/Wong e 3. A broken structure The Magellanic Clouds are not ordinary galaxies. They are irregular, dwarf galaxies, deformed by their interaction with the Milky Way. The Big Cloud is crossed by a bar of stars and is linked to the Little Cloud by a gas bridge, a filament of matter torn away by tidal forces. That bridge is witness to its gravitational dance, its slow and inexorable approach. Astronomers have discovered that the Magellanic Clouds are also surrounded by a halo of hot gas, a halo that extends far beyond their visible disk and is being torn away by the Milky Way. This gas, heated to temperatures of millions of degrees, is the result of tidal forces, but also of supernovae that explode within the Clouds. It is a spectacle of destruction, but also of creation: the gas extracted from the Clouds will one day enrich the Milky Way, which will form new stars from its ashes. 4. A tragic fate The Magellanic Clouds are doomed. They have orbited the Milky Way for billions of years and will eventually be absorbed, torn apart, digested. The Big Cloud could survive a few more billion years, but the Little Cloud is already being dislocated. Numerical simulations show that within a few billion years there will be nothing left of the Clouds but a stream of stars and gas, a river of light that runs through the halo of the Milky Way. This ending is inevitable. It is inscribed in gravity, in the dance of galaxies. But it is also a birth. Because the stars of the Clouds, their gases, their dust, will come to enrich our galaxy. They will form new stars, new planets and perhaps new lives. The Magellanic Clouds will not disappear. They will transform. They will become part of us. 5. Why observe them The Magellanic Clouds are a treasure for astronomers. They are close and, therefore, easy to study. They are young and, therefore, rich in massive stars, in nebulae, in supernovae. They are deformed, and therefore show us the effects of tidal forces, of galactic interactions. They are doomed and therefore remind us of the fragility of everything, even galaxies. For amateur astronomers in the southern hemisphere, the Magellanic Clouds are an unforgettable spectacle. The Big Cloud, with its glow stick and Tarantula, is visible to the naked eye as a milky blob detached from the Milky Way. The Little Cloud, more discreet, is a faithful companion. And between the two, the gas bridge, invisible to the naked eye, unites the two galaxies like a cosmic silk thread. 6. The Watcher’s Lesson Dear readers, the Magellanic Clouds teach us fragility and beauty. They remind us that galaxies, like beings, are born, live and die. They remind us that destruction is sometimes a form of creation, that the death of one galaxy is the birth of another. They remind us that we too are stardust and that our galaxy, the Milky Way, is itself the result of the destruction of smaller galaxies. I left my flashlight. It flickers softly, like the Magellanic Clouds dancing around our galaxy. Basketball is in its place. And I think of Jocelyne, who is horrified by her president’s cowardice and who feels sorry for you, dear Americans. He wishes that real Americans, those who still believe in democracy, could counter this boorish criminal. Me too. Because of the beauty of the cosmos, the greatness of the galaxies, the fragility of the Magellanic Clouds, all this reminds us that freedom, like light, is a fragile treasure that must be protected. The next time you look up at the southern sky, remember: out there in Dorado and Mensa, two clouds of light dance around our galaxy. They are beautiful. They are condemned. And, at this very moment, they are becoming a part of us. To read more stories from the Swiss, click on the photo, Jecelyne et Jessica in Paranal, 2024 Prenez Soin de vous mes amis et à bientôt François Click on me to read more HistoryPhoto Privée
