It is unclear what energy sources were responsible for the reionization of hydrogen atoms in the intergalactic medium 13 billion years ago. Measuring the upper limit on the number of ionizing photons produced by quasars has revealed that the contribution of quasars to reionization is negligible, suggesting that galaxies are the major energy sources.

中文翻译：

---

确认宇宙再电离的能量来源

目前尚不清楚是什么能源导致了 130 亿年前星系际介质中氢原子的再电离。测量类星体产生的电离光子数量的上限表明，类星体对再电离的贡献可以忽略不计，这表明星系是主要的能源。