The Large-Scale Structure of the Universe

Most of the mass of most galaxies is actually in dark matter like 80 to 90 percent. That's pretty difficult to measure because it's diffuse. One way we can do it is by looking at quasars quasars send out these bright rays of lightThese like pencil beams of light and when they pass through these filaments they get distorted, diffracted or bent. In some cases we have these beams that penetrate this cosmic web and give us a measurement for what's there though it can be pretty tricky and those are pretty rare.