S. Casanova

Dark matter is like an invisible glue that holds galaxies together. It emits no light, but if its particles collide, gamma rays can flash. Scientists hunted for such flashes in dwarf galaxies — small stellar clusters with lots of dark matter and almost no ordinary matter.

Imagine a huge stadium packed with people dressed in black. You're standing outside, trying to figure out what's happening inside, even though you can't see a single person. But if two people bump into each other and exchange bright T-shirts, you'd spot a flash of color.

At the center of the Milky Way, where the supermassive black hole Sagittarius A* churns gas clouds like a millstone, astronomers have caught an irregular pulse. Gamma-ray emission, the most energetic light in the universe, arrives not as a smooth wave but with a break, as if the Galaxy's heart beats with arrhythmia.