The Milky Way is much brighter than expected. It would be four to five times smaller than scientists calculate.
Hervé Poirier, editor-in-chief of the science magazine Epsiloon, tells us today that the Milky Way has finally been weighed. And the recent data collected by ESA’s Gaia satellite surprised many physicists and researchers.
franceinfo: The Surprise is that our Milky Way, also called Galaxy, is much brighter than expected. Explain to us…
Herve Poirier: 409,000 billion billion billion billion kilos, the equivalent of 206 billion suns: That is ultimately the mass of our Milky Way. And yes, it is four to five times less than previous reviews.
How was this measured?
We cannot balance our galaxy indirectly. The principle: The more massive a body is, the higher the speed of the objects orbiting it – otherwise they will fall on it. Except that while it is quite easy to measure these rotations in other galaxies, it is complicated for ours.
It is difficult to distinguish movements and distances as we immerse ourselves in the Milky Way. But the Gaia telescope has patiently recorded the trajectories of 1.8 billion stars over the past 10 years. This now allows us to derive the mass of our world precisely and safely.
But what should we make of this significantly reduced value?
Honestly, it’s strange. Our Galaxy is very light compared to the others. But there is something even stranger. In all other spiral galaxies, the rotation speed of the stars is approximately constant, no matter how far they are from the center. For this reason, since the 1970s, astrophysicists have hypothesized the existence of “dark matter,” which is invisible, massive, and six times more abundant than classical matter, which forms a halo around galaxies.
However, this doesn’t happen in our good old Milky Way: at the edges they rotate less quickly. As if there is three times less dark matter here than anywhere else. Well, why not? Our Milky Way could have led a particularly peaceful life with very few collisions, which would explain these oddities.
But the physicists don’t like that. They don’t like having to assume that we live in a single place and relying on models that apply everywhere but here. This makes you wonder whether we were wrong when measuring other galaxies. Or if nothing else is wrong. It’s very exciting: we’ve never gotten to know our world so well. But we’ve never understood so little what’s going on there…