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.
Female Narrator: Galaxies once were regarded as island universes, isolated realms of gas, dust, and billions of stars that were separated by distances unimaginably vast.
Male Narrator: But, no galaxy is an island. In fact, galaxies prefer company. The gravitational pull of a large massive galaxy attracts like-sized and smaller neighbors. Galaxies may gather in modest groupings like these, or congregate by the hundreds in enormous clusters.
Female Narrator: This is Abell 1689, one of the largest galaxy clusters known. This view spans some 2 million light years, or about the distance between our Milky Way galaxy and the nearest big spiral. Into this space, Abell 1689 packs more than 500 galaxies. As astronomers mapped nearby galaxy clusters, a more complete picture of cosmic structure emerged. Galaxy clusters gather in superclusters, and overlapping superclusters form chains and filaments spanning huge swaths of the sky. Welcome, to the cosmic web. This all-sky map shows structures created by more than a million nearby galaxies.
Male Narrator: Deeper studies show that this pattern continues to even greater distances. The cosmic web appears to be the backbone of our universe. The universe came into being 13.7 billion years ago. About 400,000 years later, it had cooled enough to form the first atoms. The event created a sudden pulse of light that astronomers now measure as the cosmic microwave background.
Female Narrator: But then, the universe went dark for millions of years.
Male Narrator: Eventually, hydrogen gas cooled enough to collapse and form the first stars. These stars not only re-illuminated the universe; they became the seeds of all future cosmic structure.
Female Narrator: The James Webb Space Telescope may be able to see clusters of these first stars. It may even catch a few of them dying in supernova explosions.
Male Narrator: Either the first stars or their progeny gathered into the first galaxies. These were small gas-rich dwarfs, nothing as grand as the big galaxies we see today; but, they were the building blocks of modern galaxies.
Female Narrator: As the dwarf galaxies form, collide, and merge into bigger galaxies, the cosmic web begins to take shape. With the James Webb Space Telescope, astronomers will glimpse the earliest phases of construction that led to the universe we know.
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