Is There a Blob of Dark Matter in the Universe?

We think we know what galaxies should look like when they're not distorted. And so we can use that to estimate how much distortion galaxies have. But it's very, very weak. It's hard to tell the difference between galaxy that's undistorted and slightly distorted. That's why we need like, thousands of galaxies to add this up statistically to get a sense for where the dark matter is interesting.