During the Universe’s Dark Ages, dense primordial gas absorbed and scattered light, preventing it from traveling. It was only when the first stars and galaxies began to shine in energetic UV light that the Epoch of Reionization began. The powerful UV light pierced through the Universe, creating holes in the gas and allowing light to travel freely.

New observations from the James Webb Space Telescope have shed light on this phenomenon, revealing how faint dwarf galaxies played a significant role in banishing the darkness.

One of the most significant gifts of the James Webb Space Telescope is its ability to delve back in time and answer fundamental questions about our Universe. This powerful infrared space telescope has provided astronomers with insights into the early stages of the Universe’s life and the forces that shaped it. A key question that scientists have been grappling with is the Epoch of Reionization, which marked the end of the Universe’s Dark Ages several hundred million years after the Big Bang.

Scientists have been puzzled about the source of light that triggered the Epoch of Reionization. The primordial gas that blocked light before the EOR was hydrogen, forming the Intergalactic Medium (IGM). Only higher-energy UV light could ionize hydrogen, leading astronomers to search for sources of UV light. While Population III stars and quasars were considered, it was dwarf galaxies that emerged as prime candidates due to their ability to emit Lyman Continuum (LyC) radiation, which can ionize hydrogen.

With the James Webb Space Telescope’s advanced capabilities, astronomers have been able to identify ultra-faint dwarf galaxies in the early Universe that were prolific emitters of ionizing radiation. These findings, published in a new research article in Nature, suggest that these dwarf galaxies played a crucial role in the Universe’s evolution during the Epoch of Reionization.

By emitting ionizing radiation, these dwarf galaxies created transparent hydrogen bubbles around themselves, eventually contributing to the ionization of the intergalactic medium and allowing light to permeate the Universe. This discovery highlights the significant role that these small, faint galaxies played in shaping the Universe’s history.

Lead author Hakim Atek remarked, “These cosmic powerhouses collectively emit more than enough energy to get the job done. Despite their tiny size, these low-mass galaxies are prolific producers of energetic radiation, and their abundance during this period is so substantial that their collective influence can transform the entire state of the Universe.”

Further studies using the James Webb Space Telescope and gravitational lensing are planned to gain a more comprehensive understanding of the population of dwarf galaxies in the early Universe and their contribution to the Epoch of Reionization.