Billions of light years away in a remote part of the universe, two neutron stars—the ultradense remnants of dead stars—collided. The catastrophic cosmic event sent light and particles, including a sudden flash of gamma rays, streaming through the universe. These gamma rays traveled for 8.5 billion years before reaching Earth.

In a new study, our team of astrophysicists examined this gamma-ray signal. We learned that the stellar collision it came from was likely caused by an even more catastrophic encounter—a merger between two galaxies.

This is the first time astronomers associated this type of signal with such a large-scale galactic interaction. Our finding offers new insight into how stellar collisions spread metals across the universe.