“The Milky Way is like an island. Beyond, it is not an ocean, but an almost empty intergalactic environment”, by astrophysicist Annie Robin – Libération

Distinguished by the Academy of Sciences in 2024, the researcher at the University of Franche-Comté spent forty years developing a “galaxy model”: which has become a reference, it is used in numerous space missions. She explains that it is when reality does not fit with the model that we put our finger on something new.

For more than forty years, the Milky Way, our galaxy, has been my main subject of research. The Milky Way is what we see in a summer sky, far from cities and stray lights, in the form of a milky streak. By observing it with the naked eye, we don't necessarily imagine that it's our galaxy!

What is a galaxy? It is a collection of stars, gas, dust and dark matter, which are held together by gravitational forces. You have to imagine a very thin and immense disk or pancake, approximately 10,000 light years in diameter, surrounded by a “halo” of much finer density, but ten times larger. Our galaxy is estimated to contain around 150 billion stars. It's a pretty typical galaxy. Our star, the Sun, is located in the disk, far from the center of this system, rather towards the edge, which means that if we look towards the center of the pancake, we see it from the edge. It forms this whitish streak in the sky, very rich in stars. By their large number, they give this diffuse light which we call the Milky Way. On the contrary, when we look in the direction opposite the center, the density of stars is more tenuous, and we no longer see the edge.

With rare exceptions, the stars visible to the naked eye are stars in our galaxy. When you look at the sky, it's hard to imagine how far away the stars are. There are some very close and some very far away. But far away