Scientists have finally figured out what turned the lights on at the dawn of time

For decades, astronomers have sought to understand a pivotal moment in cosmic history — what exactly “turned on the lights” in the universe after the Big Bang? A new study offers the most compelling answer yet: early dwarf galaxies, small but intensely luminous, may have been responsible for igniting the so-called cosmic dawn.

This epoch, known as the “era of reionization,” took place between 200 million and 1 billion years after the Big Bang. During this time, light from the first stars and galaxies ionized the surrounding hydrogen gas, transforming the opaque universe into one where light could travel freely. According to a report published by ScienceAlert, astronomers now believe that dwarf galaxies played the central role in this transformation.

Using data from the James Webb Space Telescope, researchers observed faint, distant galaxies from the early universe that were rich in hot, young stars. These galaxies produced high levels of ultraviolet radiation, strong enough to ionize the hydrogen gas around them. Crucially, their small size and porous structure made it easier for this ionizing radiation to escape into space — unlike larger galaxies, where radiation tends to get trapped by dense clouds of gas and dust.

The team also found that this reionization was not uniform. Instead, it occurred in isolated pockets of space, creating expanding “bubbles” of light that gradually overlapped. This patchwork process continued until the entire universe became transparent to light, allowing cosmic structures to evolve and become visible across vast distances.

Prior to reionization, the universe was filled with neutral hydrogen that absorbed all light — making it dark and impenetrable. Only after this transformation could photons travel freely, leading to the formation of galaxies, stars, and eventually planets. Understanding this phase is crucial for grasping how the cosmos evolved into its current structure.

The discovery underscores the importance of the James Webb Space Telescope, which is uniquely equipped to peer into the deep infrared and detect ancient light from the earliest epochs of the universe. These observations are helping scientists reconstruct the timeline of cosmic events with unprecedented clarity.

By pinpointing the sources that lit up the early universe, scientists are answering one of the most fundamental questions in cosmology. The revelation not only enhances our understanding of how the universe became visible — it also deepens our connection to the cosmic forces that made existence itself possible.