Finding Darkness In The Light: How Vera Rubin Changed The Universe
“Instead, the speeds rose rapidly, but then leveled off. As you moved farther away from a galaxy’s core, the stars’ rotation speeds didn’t drop, but rather leveled off to a constant value. The rotation curves, unexpectedly, were flat. Rubin’s work began in the Andromeda galaxy, our closest large, galactic neighbor, but quickly was extended to dozens of galaxies, which all showed the same effects. Today, that number is in the thousands, and our multiwavelength, advanced surveys have shown that it can’t be missing atoms, ions, plasmas, gas, dust, planets or asteroids that account for the mass. Either something is screwy with the laws of gravity on galactic (and larger) scales, or there’s some type of unseen mass in the Universe.”
When you look at a galaxy in the night sky, it’s easy to imagine that it’s just a system of masses like our Solar System, except on a larger scale. Instead of a single, central mass, you have many stars responsible for the galaxy’s gravitational pull. The stars revolving around the galactic center feel the tug from all the other stars and orbit accordingly, with the inner stars orbiting quickly and the outermost ones – the ones most distant from the gravitational sources – orbiting more slowly, just like the planets. At least, that’s what you’d expect. But when the techniques and the technologies for measuring this finally came to fruition, the result was a colossal surprise: the stars in a galaxy didn’t determine the galaxy’s mass or rotation properties. In fact, if you went out and measured the gas, dust, plasma, planets and everything else we can observe in the galaxy, they don’t explain it either. Something unseen and invisible was influencing the way galaxies behave.