We have finally succeeded in weighing the Milky Way

Hervé Poirier, editor-in-chief of the scientific journal Epsilon Today he explains that the Milky Way has finally been weighed. The latest data, collected by the European Space Agency’s Gaia satellite, surprised many physicists and researchers.

France Info: Surprisingly, our Milky Way galaxy, also called galaxy, is much lighter than expected. Explain to us…

Hervé Poirier: 409,000 billion billion billion billion billion kilometers equivalent to 206 billion suns: vAnd here is finally our road block milky. And yes, it is 4 to 5 times lower than previous valuations.

How was this measured?

Indirectly – we cannot place our galaxy on a large scale. Principle: The greater the mass of an object, the more objects will be attracted around it Have high speed – otherwise they will end up falling on him. Except that as much as it is very easy to measure these cycles in other galaxies, it is complicated for our own galaxy.

Movements and distances are difficult to discern, as we are immersed within the Milky Way. But no Gaia telescope He patiently collected the tracks of 1.8 billion stars for 10 years. This now allows us to deduce the mass of our universe with precision and certainty.

But what should we think about this dramatically low value?

Honestly, this is weird. Our galaxy is very light compared to other galaxies. But there is something even stranger. In all other spiral galaxies, the rotation speed of the stars is approximately constant, regardless of their distance from the center. This is what prompted astrophysicists, since the 1970s, to assume the existence of “dark matter,” which is invisible and massive, and six times more abundant than classical matter, which forms a halo around galaxies.

However, that’s not what It happens in the good old Milky Way: it rotates at a slower speed in the outskirts. As if there is three times less dark matter here than anywhere else. Well, after all, why not. Our Milky Way Galaxy would have had a particularly peaceful life, with very few collisions, which explains these anomalies.

But physicists don’t like that. They don’t like to assume that we live in one place and rely on models that are valid everywhere but here. So they began to wonder whether we were wrong about our measurements of other galaxies. Or if nothing else is wrong. It’s very exciting: we’ve never known our world so well before. But we understand little of what is happening there.