Though the Big Bang is often visualized as a burst of energy and light, for nearly half a billion years after the birth of the universe, there was no light - no stars or galaxies. Scientists have long wondered how the very first stars and galaxies formed, and now, using data from the Webb Telescope and other sensors, NASA scientists are answering that question.

In the very early universe, fundamental particles weren’t bound together. Protons and electrons weren’t bound together, and these free particles immediately scattered any traveling light waves, rendering the early universe dark. Once the universe expanded and cooled enough for the fundamental particles to join together, stable hydrogen atoms became abundant. Light wasn’t scattered so easily, and the universe went from being dark to having a “glow.” Scientists have captured and mapped this early light. It’s what we know as the “cosmic microwave background,” an energetic echo left over from the early universe.

Once matter began to cluster together, stars could form. The earliest stars were massive and bright – with a hundred-fold the mass and a million-fold the brightness of our Sun! They didn’t last long, though. Burning their fuel up in just a few million years (a blink of time on the cosmological scale), the earliest stars became explosive supernova, spewing ultraviolet light back into space - in some cases, stripping matter back into its fundamental particles in a process called “reionization.” Evidence of this return to a more “primitive” state suggests that the earliest stars must have formed before the universe was a billion years old, though scientists can’t pinpoint exactly when.

The process that fueled the stars – nucleosynthesis – fused lighter elements into heavier elements, up to the weight of iron. The periodic table, though, includes many elements heavier than iron. Scientists believe these heavier elements, including some necessary to support human life, were formed from the strong pressure waves created when stars exploded and then matter reformed, as in the reionization process. This means we all have within us matter from stars that, long ago, went nova.

Once there were stars in the universe, there were discrete and specific sources of light. At the same time, stars that had lived and died might have collapsed and formed black holes. These objects were the initial gravitational “seeds” that shaped the later morphology (shape and structure) of the universe. Early black holes had a long time to grow and merge together to form the huge black holes found at the center of massive galaxies.

NASA scientists are using the Webb Telescope to try to pinpoint when and how reinionization occurred, which sources caused it, where the first galaxies were, and what these “newborn galaxies” looked like.

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