When a massive star runs out of fuel, its core collapses and a shock wave races outward. But even before the star tears apart, particles that barely interact with ordinary matter may be born in its depths. If they decay into light, that energy leaks into the dense gas around the star.

This gas, like a blanket, wraps the star. The injected energy heats it, and the gas begins to shine like a hot lightbulb. Such light could be spotted before the main flash. Astronomers tested this on the supernova SN 2023ixf: early observations showed no extra glow. So candidate particles, such as dark photons, either aren't born or live too briefly.

The absence of a signal is also a result. It allowed scientists to rule out entire regions of parameter space where such particles could exist. In the future, when a supernova goes off in our Galaxy, this method could help us peer into the dark sector of the Universe.