Gigantic currents flow between galaxies. This is why they continue to grow, always forming new stars. The phenomenon had been modeled, it has now been observed.
With Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, today we explore space, with the ALMA telescope, in search of cosmic rivers, with an astronomical observation that will be a landmark.
franceinfo: Have astronomers managed to see cosmic rivers?
Mathilde Fontez: Yes, this is the expression of researchers: “cosmic rivers”, or “cosmic currents”. Of course, it is not water, but gas. And this gas was not found in our Solar System, but much further away, outside the galaxies, near one galaxy in particular, the Anthill, 12 billion light years from us.
But this gas is indeed flowing, it is a great current which stands out in the black of space. It is gigantic: it is 300,000 light years long, it is 3 times the diameter of our galaxy. It was seen by the ALMA radio telescope, one of the most powerful in the world, located in Chile, by an international team.
This gas flows into intergalactic space?
Yes, it’s flowing out of the galaxy, and it’s diving in. In fact, astrophysicists suspected the existence of such a structure. Their digital simulations, the models with which they study the universe, had shown them that these cosmic rivers must exist. There had already been indirect or incomplete observations.
But for the first time, we really see a river. Even if the image is a little cryptic: it looks like a succession of blurry bubbles, lined up one behind the other. This confirms that these rivers must be everywhere, between all the galaxies. Ultimately, the universe is not a collection of very compact galaxies and the void around them. Rivers flow everywhere between the structures.
Why hadn’t we seen these cosmic rivers until then?
Because they are very cold, – 260°C. But everything that is cold shines very little, it is very difficult to see with a telescope. And also because they are very thin: you should not imagine a furious flood. These rivers are more like volutes: their density is a billion billion times, less than that of the air you breathe. But it is in this very fine current that lies the resolution of a great mystery: it had been posed since the 1950s: why do galaxies still form stars?
Why was our Sun born, when our old galaxy, normally, should no longer have gas to give birth to new stars? The answer lies in these cosmic rivers: they are what supply the galaxies with matter, and which allow them to concentrate new clouds of gas, which collapse into stars. Basically, it is thanks to these cosmic rivers that we are here.