The First Stars May Shed Light on Dark Matter

The nature of the dark matter is one of the longest-standing puzzles in cosmology. Astronomers have established that dark matter is the dominant constituent of matter in the Universe, but they are still in the dark about its identity. A possible clue may have been uncovered by recent observations of the cosmic dawn—the epoch when the first stars formed (Fig. 1). Earlier this year, researchers reported a surprisingly strong absorption signal coming from gas activated by light from the first stars [1]. Now, a series of new papers [2–5] has explored what might be inferred about dark matter from this unexpected absorption. For example, the absorption could be explained by assuming that dark matter carries a small electric charge that allows it to interact weakly with ordinary matter. On the flip side, the absorption is inconsistent with certain models that predict dark matter should annihilate with itself. Regardless of the final interpretation, the cosmic dawn has clearly opened a new path toward resolving the dark matter puzzle.