cosmic-web

Gravitational lensing, the deflection of light by mass, was predicted by general relativity and first measured during the 1919 solar eclipse. Strong lensing produces Einstein rings and multiple images, weak lensing maps dark matter statistically, and microlensing reveals planets through brief brightenings of background stars.

Zoom out far enough and galaxies stop looking scattered. They trace a web of filaments, walls, clusters, and voids that spans hundreds of millions of light-years. Here is how it formed, how it was mapped, and what it is made of.

Something enormous is pulling the Milky Way, Andromeda, and thousands of other galaxies in one direction at roughly 600 km/s. For decades it hid behind the Milky Way's dust. What astronomers found when they looked was not what they expected.