What happens when two white dwarfs collide and explode?

When two carbon-oxygen white dwarfs merge violently, one ignites through direct impact, creating a supernova with a unique signature. Using detailed 3D models with careful treatment of how atoms ionize under extreme conditions, researchers find that violent mergers produce oxygen emission and ionization patterns absent from 1D simulations—and distinctly different from the leading alternative scenario (double-detonation). These predictions could be tested with the James Webb Space Telescope.