Stars & Galaxies
After 150 million years of darkness, the first stars blazed to life — and with them began the long process of building the cosmic web of galaxies we see today.
The Cosmic Dark Ages End
After the CMB was released, the universe plunged into darkness for roughly 150 million years. There were no stars, no light — just hydrogen gas slowly clumping under gravity. Then, in the densest regions, gas clouds collapsed under their own weight, heating up until nuclear fusion ignited. The universe's first light was born.
Population III Stars — The First Generation
These were the universe's original stars — enormous, luminous, and made almost entirely of hydrogen and helium. With masses 100 to 1000 times that of our Sun, they burned hot and fast, living only a few million years. When they died in supernova explosions, they seeded the universe with the first heavy elements: carbon, oxygen, iron — the building blocks of planets and life.
Galaxy Formation
Galaxies did not form from a single collapse. Instead, dark matter — an invisible form of matter making up 27% of the universe — formed a web-like cosmic scaffold. Gas and stars fell into dark matter halos, forming small proto-galaxies that merged over billions of years into larger structures. The Milky Way itself formed from dozens of such mergers.
The Role of Dark Matter
Without dark matter, galaxies as we know them would not exist. Ordinary matter alone would not provide enough gravitational pull to form stars fast enough, or hold galaxies together. Dark matter — detected only through its gravitational effects — was the invisible architect of cosmic structure. It formed the scaffolding upon which all visible matter was assembled.
The Milky Way
Our home galaxy is a barred spiral approximately 100,000 light-years in diameter, containing 200–400 billion stars. It formed roughly 13.6 billion years ago and has grown through mergers with smaller galaxies. At its center lies Sagittarius A*, a supermassive black hole with a mass of 4 million Suns. Earth orbits about 26,000 light-years from the center.
Stellar Nucleosynthesis — We Are Made of Stardust
Every element heavier than lithium was forged inside stars. When massive stars die in supernovae, they scatter these elements — carbon, oxygen, nitrogen, iron — across space. New stars and planets form from this enriched gas. The calcium in your bones, the iron in your blood, the oxygen you breathe — all were created in the heart of a dying star billions of years ago. You are made of stardust.