Scientists have just solved one of the universe’s oldest mysteries
For a long time, scientists have been trying to answer a fairly basic question about the universe: when did the lights “go on”? Not metaphorically. Literally.
Right after the Big Bang, the universe was not the glowing, star-filled place people imagine. It was dense, hot, and filled with charged particles that scattered light in all directions. Even when things cooled enough for atoms to form, space remained weak. There were no real light sources yet. Just a massive stretch of hydrogen gas waiting for something to happen. Then at some point it did.
This period is known as the “cosmic dawn,” when the first stars and galaxies formed and began pumping out radiation powerful enough to change the state of the universe itself. That radiation removed electrons from hydrogen atoms, a process called reionization, and suddenly light could travel freely. The fog lifted. The universe became visible.
The question has always been what actually drove that shift.
For years, scientists assumed it must be something big and intense. Massive galaxies. Hungry black holes blast energy into space. That scale felt right for a moment that rewired the entire universe. New research suggests otherwise.
What turned on the lights?
Using data from the James Webb Space Telescope and the Hubble Space Telescope, an international team of astronomers peered deep into a region of space known as Abell 2744, where gravity acts as a natural magnifying lens. What they found was not a handful of giant cosmic engines, but a swarm of small dwarf galaxies. Many of them.
These galaxies are small, faint and easy to miss, which is part of the reason they have been overlooked for so long. But according to the data, they were everywhere in the early universe, outnumbering larger galaxies by about 100 to 1. More importantly, they produced far more high-energy radiation than expected.
“Despite their small size, these low-mass galaxies are prolific producers of energetic radiation,” astrophysicist Hakim Atek said in a statement attached to the research published in Nature. “Their collective influence can transform the entire state of the universe.”
In other words, what turned the cosmic light switch might not have been a few dominant forces. It could have been a massive crowd of little ones all working at once.
It’s a strangely satisfying answer. The breakthrough could have come from countless small galaxies that have turned into something universe-changing.
There is still more to confirm. This research focused on one region of the sky, and researchers want to know if the same pattern appears everywhere else. But for the first time, the picture of how the universe went from dark to visible is starting to come into focus.
