Throw pebbles along a tight row of posts: they ricochet into a dense spray. Throw at an angle, and they scatter. Gamma rays in a crystal do the same: they spawn particle cascades that spread out unless the crystal’s atomic rows are perfectly aligned. Align them within a hair’s width, and the cascade sharpens into a tight beam. A small crystal then outperforms a large one.

Known since the 1970s, this alignment trick was dismissed as too finicky for telescopes. Now, it promises lighter, sharper observatories. A crystal detector can measure a gamma ray’s polarization, the direction of its vibration, to map magnetic fields around black holes and neutron stars. It also amplifies faint signals from dark matter collisions.

The surprise? A misalignment of just a few atoms’ width kills the effect. That’s why this clever idea sat unused for half a century — until now.